Fig. 8|.

Overview and proposed model for regulation of CxcA and Sle1 expression on the transcriptional, post-transcriptional and post-translational level. Transcriptional regulation: the cxcA and sle1 genes are both regulated by the two-component systems WalKR and GraSR, where the response regulators WalR or GraR, upon phosphorylation bind to the promoter (P) of sle1 or cxcA to activate transcription of the genes. The regulatory RNA, Rbc1 is transcribed from the opposite strand of the cxcA gene. Post-transcriptional regulation: The Rbc1 asRNA binds in cis to the cxcA mRNA and in trans to the CHAP domain region of the sle1 mRNA. To allow time for Rbc1 binding, transcription and translation are uncoupled through mechanism that delay translation initiation, including the folding of the 5′ end of the cxcA mRNA into a temperature-dependent secondary structure that covers the Shine-Dalgarno sequence (Hussein et al., 2019). Likewise the folding of sle1 mRNA can be computationally predicted using PASIFIC (Millman et al., 2017). Additionally, translation is delayed by the use of rare, inefficient start codons UUG in cxcA mRNA, and GUG in the sle1 transcript. Post-translational regulation: Sle1 and CxcA are substrates of the ClpXP protease (Feng et al., 2013). FtsK protects CxcA and Sle1 from ClpXP degradation during the cell cycle (Veiga et al., 2023). Moreover, Rbc1 has a role in protecting CxcA and Sle1 from ClpXP proteolysis, particularly at low temperatures. See main text for details.