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tmRNA Is Required for Correct Timing of DNA Replication in Caulobacter crescentus. Kenneth C. Keiler, 2003.SsrA, or tmRNA, is a small RNA that interacts with selected translating ribosomes to target the nascent polypeptides for degradation . Here we report that SsrA activity is required for normal timing of the G1-to-S transition in Caulobacter crescentus . A deletion of the ssrA gene, or of the gene encoding SmpB, a protein required for SsrA activity, results in a specific delay in the cell cycle during the G1-to-S transition . The ssrA deletion phenotype is not due to accumulation of stalled ribosomes, because the deletion is not complemented by a mutated version of SsrA that releases ribosomes but does not target proteins for degradation . Degradation of the CtrA response regulator normally coincides with initiation of DNA replication, but in strains lacking SsrA activity there is a 40-min delay between the degradation of CtrA and replication initiation . This uncoupling of initiation of replication from CtrA degradation indicates that there is an SsrA-dependent pathway required for correct timing of DNA replication . Analysis of the Ferric Citrate Transport Gene Promoter of Escherichia coli. Sabine Enz, 2003.FecI, an extracytoplasmic-function  factor, is required for initiation of transcription of the ferric citrate transport genes . A mutational analysis of the fecA promoter revealed that the nonconserved -10 region and a downstream regulatory element are important for fecA promoter activity . However, nucleotide substitutions in the well-conserved -35 region also have an effect on the fecA promoter activity . Titration of FecI suggests that the FecI-RNA polymerase holoenzyme does not bind strongly to the downstream regulatory element, which is therefore probably involved in a subsequent step of transcription initiation .
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