Thermoregulation of the pap operon: evidence for the involvement of RimJ, the N-terminal acetylase of ribosomal protein S5.

Our previous work showed that pap pilin gene transcription is subject to a thermoregulatory control mechanism under which pap pilin is not transcribed at a low temperature (23 degrees C) (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). In order to isolate genes involved in this temperature regulation of gene expression, chromosomal mini-Tn10 (mTn10) mutations that allowed transcription of the pap pilin gene at 23 degrees C were identified, and the locus was designated tcp, for "thermoregulatory control of pap" (C. A. White-Ziegler, L. B. Blyn, B. A. Braaten, and D. A. Low, J. Bacteriol. 172:1775-1782, 1990). In the present study, quantitative analysis showed that the tcp mutations restore pap pilin transcription at 23 degrees C to levels similar to those measured at 37 degrees C. By in vivo recombination, the tcp mutations were mapped to phage E4H10S of the Kohara library of the Escherichia coli chromosome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987). The tcp locus was cloned by complementation, in which a 1.3-kb DNA fragment, derived from the Kohara phage, was shown to restore thermoregulation to the mTn10 mutants. DNA sequencing revealed two open reading frames (ORFs) encoding proteins with calculated molecular masses of 22.7 and 20.3 kDa. The sequence of the 22.7-kDa ORF was identical to that of rimJ, the N-terminal acetylase of the ribosomal protein S5. The gene encoding the 20.3-kDa ORF, designated g20.3 here, did not display significant homology to any known DNA or protein sequence. On the basis of Northern (RNA) blot data, rimJ and g20.3 are located within the same operon. Two of the mTn10 transposons in the thermoregulatory mutants were inserted within the coding region of rimJ, indicating that the RimJ protein plays an important role in the temperature regulation of pap pilin gene transcription. However, rimJ itself is not thermoregulated, since rimJ transcripts were detected at both 23 and 37 degrees C. Disruption of the g20.3 gene by insertion and deletion mutagenesis did not affect thermoregulation of the pap operon, suggesting that, although g20.3 lies within the same operon as rimJ, it does not play a role in thermoregulation.