Bacteriophage P4 sut1: a mutation suppressing transcription termination.
In the Escherichia coli satellite phage P4, transcription starting from PLE is prevalently controlled via premature termination at several termination sites. We identified a spontaneous mutation, P4 sut1 (suppression of termination), in the natural stop codon of P4 orf151 that, by elongating translation, suppresses transcription termination at the downstream t151 site. Both the translational and the transcriptional profile of P4 sut1 differed from those of P4 wild-type. First of all, P4 sut1 did not express Orf151, but a higher molecular mass protein, compatible with the 303 codon open reading frame generated by the fusion of orf151, cnr and the intervening 138 nt. Moreover, after infection of E. coli, the mutant expressed a very low amount of the 1.3 and 1.7 kb transcripts originating at PLE and PLL promoters, respectively, and terminating at the intracistronic t151 site, whereas correspondingly higher amounts of the 4.1 and 4.5 kb RNAs arising from the same promoters and covering the entire operon were detected. Thus the sut1 mutation converts a natural stop codon into a sense codon, suppresses a natural intracistronic termination site and leads to overexpression of the downstream cnr and alpha genes. This correlates with the inability of P4 sut1 to propagate in the plasmid state. By cloning different P4 DNA fragments, we mapped the t151 transcription termination site within the 7633-7361 region between orf151 and gene cnr. A potential stem-loop structure, resembling the structure of a Rho-independent termination site, was predicted by mfold sequence analysis at 7414-7385.
Terzano
Susanna
S
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Oliva
Ilaria
I
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Forti
Francesca
F
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Sala
Claudia
C
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Magnoni
Francesca
F
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Dehò
Gianni
G
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Ghisotti
Daniela
D
Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
D018388:Codon, Terminator / Q000235:genetics; D003090:Coliphages / Q000235:genetics*; D004926:Escherichia coli / Q000821:virology*; D020869:Gene Expression Profiling; D009154:Mutation; D017900:Myoviridae / Q000235:genetics*; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012367:RNA, Viral / Q000032:analysis / Q000235:genetics; D012526:Satellite Viruses / Q000235:genetics*; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000032:analysis / Q000235:genetics
D018388:Codon, Terminator; D012333:RNA, Messenger; D012367:RNA, Viral; D014764:Viral Proteins