Transcriptional organization and regulation of a polycistronic cold shock operon in Sinorhizobium meliloti RM1021 encoding homologs of the Escherichia coli major cold shock gene cspA and ribosomal protein gene rpsU
Kp. O'Connell et Mf. Thomashow, Transcriptional organization and regulation of a polycistronic cold shock operon in Sinorhizobium meliloti RM1021 encoding homologs of the Escherichia coli major cold shock gene cspA and ribosomal protein gene rpsU, APPL ENVIR, 66(1), 2000, pp. 392-400
A homolog of the major eubacterial cold shock gene cspA was identified in S
inorhizobium meliloti RM1021 by luxAB reporter transposon mutagenesis, Here
we further characterize the organization and regulation of this locus. DNA
sequence analysis indicated that the locus includes three open reading fra
mes (ORFs) encoding homologs corresponding to CspA a novel 10.6-kDa polypep
tide designated ORF2, and a homolog of the Escherichia coli ribosomal prote
in 821, Transcription analysis indicated that this locus produced two diffe
rent-sized cspA-hybridizing transcripts upon cold shock, a 400-nucleotide (
nt) RNA encoding cspA alone and a 1,000-nt transcript encoding cspA-ORF2-rp
sU. The sizes of the transcripts agreed with the location of the transcript
ion start site determined by primer extension and the locations of two puta
tive transcriptional terminators. The promoter of the csp,4-ORF2-rpsU locus
had -10 and -35 elements similar to the E. coli sigma(70) consensus promot
er and, like the cspA locus of E. coli, included an AT-rich region upstream
of the -35 hexamer. The promoter of the S. meliloti cspA locus was found t
o impart cold shock-induced mRNA accumulation, In addition, the 5'-untransl
ated region (5' UTR) was found to increase the fold induction of cspA trans
cripts after cold shock and depressed the level of lux LB mRNA prior to col
d shock, another feature similar to cspA regulation in E, coli, No "cold bo
x" was identified upstream of the S. meliloti cspA gene, however, and there
was no other obvious sequence identity between the S. meliloti 5' UTR and
that of E, coli, DNA hybridization analysis indicated that outside the cspA
-ORF2-rpsU cold shock locus there are several additional cspA-like genes an
d a second rpsU homolog.