Simplex Virus Type 1 Temperature-sensitive Mutant ts K

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1 J. gen. Virol. (1984), 65, Printed in Great Britain 859 Key words: HSV-1 ts K/marker rescue/vmw 175 Determination of the Sequence Alteration in the DNA of the Herpes Simplex Virus Type 1 Temperature-sensitive Mutant ts K By M.-J. DAVISON, 1. V. G. PRESTON 1'2 AND D. J. McGEOCH 1'2 1Institute of Virology and 2 MRC Virology Unit, University of Glasgow, Church Street, Glasgow Gll 5JR, U.K. (Accepted 7 February 1984) SUMMARY The alteration in the DNA sequence responsible for the mutant phenotype of the herpes simplex virus type 1 temperature-sensitive mutant ts K has been determined. A single C:G base pair present in the wild-type Vmw 175 immediate-early polypeptidecoding sequence has been replaced by T:A in the mutant gene. This results in the substitution of an alanine by a valine codon. In two revertants the mutant T : A base pair has been resubstituted by C : G. INTRODUCTION Lytic infection with herpes simplex virus type 1 (HSV-1) is considered to display three major temporal classes of protein synthesis, designated immediate-early, early and late (Honess & Roizman, 1974, 1975). The first of these is not dependent on previous synthesis of virus proteins. At least five immediate-early proteins have been recognized (Honess & Roizman, 1974; Preston et al., 1978; Preston, 1979b; Fenwick et al., 1980), but, in general, little is known of their function. The best studied is Vmw 175, where a number of temperature-sensitive mutant forms of the gene have been described. The mutant ts K in particular has been extensively used in studies of Vmw 175 function. Infection with this mutant at non-permissive temperature results in the over-production of immediate-early mrnas and proteins, and in a failure to synthesize early and late classes of mrnas and proteins (Marsden et al., 1976; Watson & Clements, 1978; Preston, 1979a). Under non-permissive conditions, this mutant Vmw 175 polypeptide is aberrantly processed and, unlike the wild-type protein, is not localized mainly in the cell nucleus (Preston, 1979b). Temperature shift-up experiments have shown that functional Vmw 175 is required continuously throughout infection for transcription of early genes and some late genes to proceed, and for the shut-off of immediate-early transcription (Watson & Clements, 1978, 1980; Preston, 1979a, b). Thus, it is clear that Vmw 175 has an important involvement in the regulation of virus gene expression. The gene for Vmw 175 is present in two copies in the genome of HSV-1, one copy in each of the short repeat regions (IRs and TRs; see Fig. 1) (Preston et al., 1978). Recent marker rescue studies localized the ts K mutation first to the 1844 base pair (bp) BamHI y fragment of the genome and then to a 339 bp Sau3AI subfragment of BamHI y (Preston, 1981). We have previously published the DNA sequence of the wild-type BamHI y fragment (Murchie & McGeoch, 1982) and, from our interpretation of the sequence data, the 339 bp Sau3AI fragment lies wholly within polypeptide-coding DNA. In this paper we identify by DNA sequencing the mutational event responsible for the ts K phenotype. METHODS Tissue culture ceils. BHK-2I clone 13 cells (MacPherson & Stoker, 1962) were grown in Eagle's medium supplemented with 10~ tryptose phosphate broth and 10% calf serum. Virus. The isolation of ts K, which has a syncytial (syn) plaque morphology, has been described previously (Brown et al., 1973; Crombie, 1975). A non-syncytial (syn + ) form of ts K was isolated from the cross ts K syn strain 17 syn +. This virus, ts K syn +, was used in all experiments. Ts ~ revertants, ts K rev 4 and ts K rev 5, were isolated from different plaque-purified stocks of ts K syn /84/ $ SGM

2 860 M.-J. DAVISON, V. G. PRESTON AND D. J. McGEOCH Preparation of virus DNA. HSV-I DNA was purified from cell-associated and cell-released virions as described by Wilkie (1973). Marker rescue assay. The method of Stow et al. (1978) was used as described previously (Preston, 1981). Construction of recombinant plasmids. Virion DNA preparations from ts K syn, ts K rev 4 and ts K rev 5 were digested with BamHI; the BamHI y fragments were isolated from agarose gels and cloned into the BamHI site of the plasmid vector pat 153 (Twigg & Sherratt, 1980). Hybrid plasmids were propagated in Escherichia coti H B 101. DNA sequencing. Plasmid DNAs were prepared as described previously and the BamHI y fragments isolated (Murchie & McGeoch, 1982). The Sau3AI cleavage products of BamHI y were radiolabelled at their 5' termini with [~-32p]ATP using T4 polynucleotide kinase, and uniquely end-labelled fragments of the 339 bp Sau3AI fragment were then generated by secondary cleavage. These were then used in the sequencing procedure of Maxam & Gilbert (1977, 1980). BamHI y fragments of plasmid-cloned ts K clone DNA and revertant 4 DNA were also subcloned into the BamHI site of the single-stranded phage vector M13mp8 (Messing & Vieira, 1983), and for each, a sequence of about 200 residues adjacent to the appropriate BamHI terminus was determined by the chain termination sequencing system (Sanger et al., 1980). RESULTS Checks on recombinant plasmids Plasmids carrying the BamHI y fragments from ts K syn +, ts K rev 4 and ts K rev 5 were constructed to use as substrates for DNA sequencing. These plasmids, together with a plasmid carrying wild-type BamHI y, were tested in marker rescue experiments with HSV-1 ts K syn (Table 1). The failure of cloned ts K BamHI y to give significant ts + progeny gave reassurance that the mutant DNA sequence had indeed been cloned. Separated SmaI and Hinf) fragments from the cloned DNAs of the two revertants were also tested for rescue ofts K, and it was found that the rescuing sequences were present in a region corresponding to 375 bp at the right end of BamHI y as oriented in Fig. 1, that is in the same area as the ts K mutation (data not shown). It was therefore concluded that the reversion events had occurred at or close to the site of the ts K mutation. TRt. U L IR L IR~ U s TR s I I I'-'T'-I IZ] I I D 0 B Q g J G O Q * kbp I I I I I 175 i x v q "1 I " II I Fig. 1. Structure of the Vmw 175 gene region of the HSV- 1 genome. The prototype genome orientation of HSV- 1 is shown in the upper part of the figure, and below it an expansion of part of the short region, with DNA length in kilobase pairs (kbp). The positions and orientations of the Vmw 175 mrna (arrowheaded line) and polypeptide (solid portion of line) coding sequences are indicated. The BamHI map of the region is shown and the hatched area denotes the 339 bp Sau3AI subfragment of BamHI y. ~TA

3 (a) DNA sequence change in HSV-1 ts K mutant T C G A T C G A : G (3 AGGGGC,.,., C G (b) 861 cgt AGGC AGG GGCA Fig. 2. Autoradiographs showing the nucleotide sequence alteration in the DNA of ts K. Results were obtained with the M 13 chain terminator system. (a) Sequencing products obtained from the wild-type BamHI y fragment between nucleotides 1430 and 1417 on the mrna non-sense strand; (b) sequencing products obtained from the same region of the BamHI y fragment of ts K. The altered nucleotide 1424 is underlined. The high G + C content of these sequences gives rise to some anomalous band spacings. Table 1. Marker rescue of ts K with recombinant plasmid DNA Plasmid DNA cleaved Virus derivation of Relative e.o.p. with BamHI* BamHI y fragment of progeny t - - < pgx1 ts strain 17 syn 7.0 pgx13 ts K syn pgx14 ts K rev pgx15 ts K rev * The plasmid DNAs were cleaved with BamHI before being tested for ability to rescue ts K. t Values represent relative efficiency of plating, 38.5/31 C x 102 of progeny virus from transfected cells. DNA sequence analysis The following DNA sequences were determined: (i) for ts K DNA, 343 residues representing the rightmost Sau3AI fragment ofbamhi y as oriented in Fig. 1 ; (ii) for ts K rev 5 DNA, the same region; (iii) for ts K rev 4 DNA, 146 residues representing the right terminus ofbamhi y. In this paper, DNA sequence enumeration takes the A of the presumed translation initiator ATG codon of Vmw 175 (Murchie & McGeoch, 1982) as number 1, and refers to the mrnasense strand. The region under study then comprises residues 1227 to The following results were obtained: (i) ts K DNA was identical in sequence to the wild-type, except at residue 1424 where a T residue was found in ts K and a C residue in wild-type (Fig. 2); (ii) ts K rev 5 DNA was completely identical to wild-type; (iii) ts K rev 4 DNA was identical to wild-type in the region sequenced, which includes residue The data therefore indicate that a C to T transition at residue 1424 gave rise to ts K, and that reversion in the two independent cases studied was at the same site and to the wild-type sequence. The nature of the mutation is consistent with the use of bromodeoxyuridine as mutagen in the generation of ts K. DISCUSSION Our previous assignment of codon reading frame to the region of the ts K mutation shows that the mutation changes the codon GCG to GTG, so changing residue 475 of the Vmw 175 protein from alanine to valine (Fig. 3). We note that assignment of reading frame is particularly clear in this locality, with the two other frames blocked by stop codons. We have used the computer program of Garnier et al. (1978) to predict secondary structure in this region of Vmw 175 (Fig. 3). The program assigns the mutated residue to a region of extended structure close to an c~-helical region. There is a mix of hydrophobic and hydrophilic residues nearby, with a local hydrophilic maximum around 16 residues towards the N-terminus. The surroundings of the mutable residue are thus apparently typical of globular protein structure, and no further insight into the mechanistic basis of the ts phenotype appears possible.

4 862 M.-J. DAVISON, V. G. PRESTON AND D.J. McGEOCH LAHAAAAVAMSRRYDRAQKGFLLTSLRRAYAPLLARENAALTGAAGSPGAGADDEGVAAV--- HHHHHHHHHHHHHHTTCTCEEEEEEETTTEEEHHHHHHHHHHCCCCCCCCCCHHHHHHHH (+) Fig. 3. Amino acid sequence around the ts K mutated site. Sixty amino acids of the wild-type Vmw 175 sequence are listed in single-letter code (IUPAC-IUB Commission on Biochemical Nomenclature, 1968), with numbering from the N-terminus. The ts K alteration of A to V at residue 475 is indicated. The second bottom line lists the secondary structure prediction for the wild-type sequence from the program of Garnier et al. (1978): H denotes cehelix, T denotes specific turn structure, E denotes extended structure (/3-sheet) and C denotes coil (undefined structure). On the bottom line the locations of acidic (-) and basic (+) groups are indicated. V The change Ala to Val is relatively conservative, representing the addition of two side chain methyl groups. Similar changes, representing substitution of neutral residues by bulkier side chains, but with no changes in charge, have been described as the basis of several ts mutations in other systems (Deininger et al., 1981; Thomas et al., 1981). In the present instance, such a change appears consistent with the observation that the mutant protein's inactivation at higher temperature is reversible, suggesting a minimal functional deficiency. The characterization of two independent revertants as both having changed back to the wildtype DNA sequence may seem somewhat unexpected. However, the possibilities for other classes of reversion in the same codon are limited. A first base change of GTG would give a codon for Met or for Leu, both large hydrophobic residues, whereas any third base change would generate another Val codon. Of second position changes, only that to GCG gives the wild-type Ala. Change to GAG would give a large and acidic Glu residue, whereas change to GGG would give Gly, the only apparently reasonable alternative residue. We acknowledge the critical interest of Professor J. H. Subak-Sharpe. During the course of this work, M.-J.D. was in receipt of a training fellowship from S.E.R.C. REFERENCES BROWN, S. M., RITCHIE, D. A. & SUBAK-SHARPE, J. H. (1973). Genetic studies with herpes simplex virus type 1. The isolation of temperature-sensitive mutants, their arrangement into complementation groups and recombination analysis leading to a linkage map. Journal of General Virology 18, CROMBIE, I. K. (1975). Genetic and biochemical studies with herpes simplex virus type 1. Ph.D thesis, University of Glasgow. DEININGER, P. L., LAPORTE, P. & FRIEDMANN, T. (1981). Nucleotide sequence changes in polyoma ts-a mutants: correlation with protein structure. Journal of Virology 37, FENWICK, M.,WALKER, M. & MARSHALL, L. (1980). Some characteristics of an early protein (ICP 22) synthesized in cells infected with herpes simplex virus. Journal of General Virology 47, GARNIER, J., OSGUTHORPE, D. J. & ROBSON, B. (1978). Analysis of the accuracy and implications of simple methods for predicting the secondary structure of globular proteins. Journal of Molecular Biology 120, tioness, R. W. a ROlZMAN, B. (1974). Regulation of herpesvirus macromolecular synthesis. I. Cascade regulation of the synthesis of three groups of viral proteins. Journal of Virology 14, HONESS, R. W. a ROIZMAN, B. (1975). Regulation of herpesvirus macromolecular synthesis: sequential transition of polypeptide synthesis requires functional viral polypeptides. Proceedings of the National Academy of Sciences, U.S.A. 72, IUPAC-IUB COMMISSION ON BIOCHEMICAL NOMENCLATURE (1968). A one-letter notation for amino acid sequences. Tentative rules. Journal of Biological Chemistry 243, MACPHERSON, I. & STOKER, M. (1962). Polyoma transformation of hamster cell clones - an investigation of genetic factors affecting cell competence. Virology 16, MARSDEN, H. S., CROMBIE, I. K. & SUBAK-SHARPE, J. H. (1976). Control of protein synthesis in herpesvirus-infected cells: analysis of the polypeptides induced by wild type and sixteen temperature-sensitive mutants of HSV strain 17. Journal of General Virology 31,

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