Control of Bacterial Protein Synthesis During Viral Infection 
We are attempting to test this model through a 
direct assay of bar RNA imeraction with cell com- 
ponents and the effect of Pth on polypeptide 
chain termination. We will also investigate possi- 
ble genes and gene products that interact with 
Pth through the isolation of second-site muta- 
tions that suppress pth defect. 
Biochemistry of Pth and Regulation 
of pth Expression 
To purify Pth protein, we have exploited the 
fact that cells harboring pth plasmids overpro- 
duce the wild-type enzyme. Part of our current 
efforts are devoted to overproducing and purify- 
ing mutant enzymes to compare their biochemi- 
cal properties. Mutant Pths may have different 
patterns of specificity for various amino acyl- 
tRNAs. Also our laboratory is working on the con- 
trol of pth expression by analyzing the transcrip- 
tional and translational properties of the gene. 
What Does bar Do for X? 
We have considered two possible roles for bar 
regulation in X biology, taking into account the 
two functions proposed for Pth. First, bar RNA 
may control the relative levels of specific tRNAs 
to fit the profile of codon usage in X. This func- 
tion, perfectly tolerated in normal cells, may lead 
to inhibition of phage development or to lethality 
in cells defective for Pth. Second, bar RNA may 
act on termination and/or initiation of polypep- 
tide chains directed by phage transcripts. Among 
X genes, UGA is the most frequent termination 
codon (not UAA, as in the host), and in the X 
genome it is not uncommon for a gene's termina- 
tion codon to overlap partially the initiation co- 
don of the next gene, producing the sequence 
AUGA. The fact that the bar core RNA contains 
the sequence AUGA, and the alleged interaction 
of this sequence with ribosomal 1 6S RNA, suggest 
a role for these overlapping genes in polypeptide 
chain-termination (-initiation) events. 
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