ORGANIZATION AND TRANSCRIPTIONAL ANALYSIS OF THE LISTERIA PHAGE A511 LATE GENE REGION COMPRISING THE MAJOR CAPSID AND TAIL SHEATH PROTEIN GENES CPS AND TSH

A511 is a broad-host-range, virulent myovirus for Listeria monocytogen es. The genes encoding major structural proteins of the capsid (cps) a nd tail sheath (tsh) were mapped to a 10.15-kb late gene fragment. We have determined the complete nucleotide sequence of this region and co nfirmed the identities of Cps (48.7 kDa) and Tsh (61.3 kDa) by N-termi nal amino acid sequencing of both proteins. In addition, nine other op en reading frames were identified. On the basis of amino acid sequence homologies to known phage-encoded proteins, some putative functions a nd locations could be assigned to some of the deduced gene products. W e present evidence that the cps product is proteolytically cleaved bet ween Lys-23 and Ser-24 to yield the 444-residue polypeptide found in t he mature viral capsid. We also found that the N-terminal methionine i s absent from the mature tail sheath protein. cps and tsh are late gen es; mRNAs first appear 15 to 20 min after infection of L. monocytogene s. Northern (RNA) hybridizations of total late mRNA with specific olig onucleotide probes were used to determine the sizes of respective tran scripts. Primer extension analyses enabled the positive identification of six late promoters, which were found to differ from those identifi ed in the chromosome of listeria spp. The bulk of transcripts from cps acid tsh arise from two phage promoters with identical 13-nucleotide sequences (TGCTAGATTATAG [core region underlined]) in the -10 region w hich we speculate determines specific and timed expression of these ge nes. A 123-nucleotide leader sequence at the 5' end of the cps transcr ipt was predicted to form a strong secondary structure (Delta G = -40. 7 kcal [-170.3 kJ]/mol) Our results show that the strongly expressed A 511 cps and tsh genes are included in two separate gene clusters and a re independently regulated at the transcriptional level.