## 3 Post-Transcriptional and Translational Regulation in Integrons
### Integron-Encoded Regulatory RNA  
In bacteria, sRNAs act as global regulators of mRNAs, modulating their activity at the posttranscriptional level. A recent study characterized a new mechanism in which in tandem amplification of intergon-associated gene cassettes would alter the levels of a putative small RNA (sRNA), which would regulate virulence and global gene expression in _A. baumannii_[134]. These transcripts can be derived from non-coding sequences, such as the UTRs of genes and intergenic regions, and can be independently expressed or produced by the cleavage of longer transcripts catalyzed by RNAses [136].  
Some _A. baumannii_ strains may switch between the virulent phenotype of opacity (VIR-O) and the avirulent translucent (AV-T), resulting in decreased virulence in vivo [137]. [PERSON] et al. [134] observed that a duplication of an _aadB_-containing gene cassette array in a composite class 1 trigon positively influenced the rates of switching between VIR-O and AV-T cells. However, they noticed that another bacterial subpopulation displaying a third opacity phenotype, designated low-switching opaque (LSO) variant, exhibited a remarkable reduction of switching to AV-T relative to the switching frequency of the VIR-O variants. In this case, a unique copy of _aadB_ was identified in the integer of these LSO variants, and hyper-switching to the AV-T state was only observed when the copy number of _aadB_ increased. These findings indicated that opacity switching dynamics depended on  
Figure 12: Regulation of antibiotic resistance genes by translation attenuation. The resistance gene presents a leader sequence encoding a small ORF. The translation of the leader ORF leads to the formation of a hairpin structure, inhibiting gene translation by SD sequence arresting (**top panel**). The presence of an antibiotic stalls the ribosome in the leader ORF. This event prompts the production of an additional secondary structure, enabling ribosomes to approach the SD sequence and proceed with resistance gene translation (**bottom panel**).  
the _aadB_ copy number sRNA. The element regulating this opacity switching was found to be an sRNA of \(\sim\)300 nucleotides encoded upstream the _aadB_ gene cassette, within the 5\({}^{\prime}\)CS region of class 1 integrins. Thus, this sRNA would comprise the transcript originating from Pc that included the 5\({}^{\prime}\) end of _intt11_, the _attt11_ site, and the short 5\({}^{\prime}\)UTR of _aadB_ of only 10 bp. In fact, the class 1 integer 5\({}^{\prime}\)CS region is known for harboring several regulatory signals, such as global regulator binding sites (LexA, H-NS, IHF, FIS) and the ORF-11 (also ORF-17 and ORF-18) coding segment, which could be involved with the opacity switching regulation. However, site-directed mutagenesis and transposon insertion assays revealed that none of these regulatory elements within the 5\({}^{\prime}\)CS appeared to be responsible for controlling switching rates and that this phenomenon was attributed to the production of the proposed sRNA. Despite this, the precise sRNA sequence, how it is generated and processed, its target, and its regulatory mechanism remain to be determined. Therefore, this finding is clear evidence of the versatility of integrins, which includes functions other than the acquisition and expression of antibiotic resistance gene cassettes.