The asiA gene product of bacteriophage T4 is required for middle mode RNA synthesis.
The asiA gene of bacteriophage T4 encodes a 10-kDa peptide which binds strongly in vitro to the sigma 70 subunit of Escherichia coli RNA polymerase, thereby weakening sigma 70-core interactions and inhibiting sigma 70-dependent transcription. To assess the physiological role of this protein, we have introduced an amber mutation into the proximal portion of the asiA gene. On suppressor-deficient hosts, this mutant phage (amS22) produces minute plaques and exhibits a pronounced delay in phage production. During these mutant infections, T4 DNA synthesis is strongly delayed, suggesting that the AsiA protein plays an important role during the prereplicative period of phage T4 development. The kinetics of protein synthesis show clearly that while T4 early proteins are synthesized normally, those expressed primarily via the middle mode exhibit a marked inhibition. In fact, the pattern of protein synthesis after amS22 infection resembles greatly that seen after infection by amG1, an amber mutant in motA, a T4 gene whose product is known to control middle mode RNA synthesis. The amber mutations in the motA and asiA genes complement, both for phage growth and for normal kinetics of middle mode protein synthesis. Furthermore, primer extension analyses show that three different MotA-dependent T4 middle promoters are not recognized after infection by the asiA mutant phage. Thus, in conjunction with the MotA protein, the AsiA protein is required for transcription activation at T4 middle mode promoters.
Department of Biological Sciences, State University of New York at Buffalo 14260.
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Ouhammouch
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Orsini
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Brody
D017122:Bacteriophage T4 / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D005814:Genes, Viral / Q000235:genetics*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009154:Mutation; D012367:RNA, Viral / Q000096:biosynthesis*; D012808:Sigma Factor / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics*; D014779:Virus Replication / Q000235:genetics
C078876:AsiA protein, Enterobacteria phage T4; D004268:DNA-Binding Proteins; C067996:MotA protein, Enterobacteria phage T4; D012367:RNA, Viral; D012808:Sigma Factor; D014157:Transcription Factors; D014764:Viral Proteins; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases