C. Ranquet et al., The tRNA function of SsrA contributes to controlling repression of bacteriophage Mu prophage, P NAS US, 98(18), 2001, pp. 10220-10225
Citations number
47
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The small regulatory RNA SsrA has both tRNA and mRNA activities. It charges
alanine and interacts with stalled ribosomes, allowing for translation to
resume on the SsrA mRNA moiety. Hence, unfinished peptides carry a short am
ino acid tag, which serves as a signal for degradation by energy-dependent
proteases. In SsrA-defective Escherichia coli strains, thermoinducible muta
nts of the transposable bacteriophage Mu (Mucts) are no longer induced at h
igh temperature. Here we show that truncated forms of the key regulator of
Mu lysogeny, the repressor Repc, accumulate in the absence of SsrA. These f
orms resemble C-terminally truncated dominant Mu repressor mutants previous
ly isolated from Mucts, which are no longer thermoinducible and bind operat
or DNA with a high affinity even at high temperature. Using various ssrA al
leles, we demonstrate the importance of SsrA charging on the ribosome for c
ontrolling Mu prophage repression. Our results thus substantiate the previo
us observation that trans-translation is not the only function of the SsrA.
The alternative function of SsrA appears to influence the stability of Mu
lysogens by controlling the translation of the C-terminal domain of the rep
ressor protein, which modulates the affinity of the protein for DNA and its
susceptibility to proteolytic degradation.