5.4) Lrp is the target of several regulations by sRNA
The expression level of E. coli lrp is controlled by
different proteins and environmental conditions. H-NS and the
nitrite-sensitive repressor NsrR could repress the transcription of thelrp gene (Oshima et al. , 1995; Partridge et al. ,
2009), whereas GadE and the alarmone ppGpp activate the expression oflrp during amino acid starvation (Hommais et al. , 2004;
Traxler et al. , 2011). Furthermore, the lrp gene is
autoregulated (Wang et al. , 1994), and it has been reported that
arginine-loaded ArgR indirectly interferes with the negative
autoregulation of lrp (Torres Montaguth et al. ,
2019).
In E. coli and S. enterica, the location of the
transcription start site is more than 250 nt upstream of the start
codon, making this 5’UTR a desirable site for sRNA binding and
regulation (Wang et al. , 1994; McFarland and Dorman, 2008).
Wright et al., (2013) developed CopraRNA, an algorithm that uses
comparative genomics to predict mRNA targets for bacterial small RNAs.
Indeed, they identified lrp as a putative target of 7 sRNAs:
GcvB, MicF, DsrA, FnrS, MicA, MicC, and RprA-L. Experimental validation
was performed on GcvB, MicF and DsrA. In addition, a novel sRNA called
ArcZ, was discovered to post-transcriptionally repress lrp inErwinia amylovora (Figure 4a-b ) (Schachterle and Sundin,
2019). These regulations will be reviewed below.