# Protein Assistants of Small Ribosomal Subunit Biogenesis in Bacteria
## 2 30S Ribosomal Subunit Biogenesis Factors
### Hfq  
The host factor for Q\(\beta\) replication (Hfq) is a new ribosome biogenesis factor. Hfq was discovered to be one of the _E. coli_ proteins required for in vitro replication of the Q\(\beta\) bacteriophage [107]. Hfq melts the secondary structure of the phage RNA, facilitating its interaction with the Q\(\beta\) replicase [108]. Hfq is a highly conserved thermostable hexameric protein with a 12 kDa molecular mass for the monomer in _E. coli_. [109]. The Hfq monomer possesses a characteristic Sm fold that consists of the N-terminal \(\alpha\)-helix and the five-strand antiparallel \(\beta\)-sheet (Figure 3h) [110]. It belongs to the Sm/Lsm superfamily of eukaryotic and archaeal proteins [111; 112; 113]. In eukaryotes, these proteins form ringlike hexa/heptamers, and are components of the spliceosome in which they mediate RNA-RNA contacts required for mRNA splicing [114]. The function of archaeal Sm/Lsm proteins is still unknown. In noninfected bacterial cells, Hfq controls the expression of various genes by facilitating imperfect base pairing between small regulatory RNAs (sRNAs) and their mRNA targets [115; 116; 117; 118], acting as an RNA chaperone. Presumably, the role of Hfq is not limited to the control of gene expression, as there is evidence that the RNA chaperone activity of Hfq is required in other cellular processes. It was shown that Hfq was involved in mRNA polyadenylation [119], regulation of virulence-factor synthesis [120], and even the formation of the bacterial nucleoid [121].  
Recent data revealed a novel role for Hfq. [PERSON] and coauthors demonstrated that hfq knockout in _E. coli_ conferred the cold-sensitive phenotype (slow growth of the \(\Delta\)hfq cells at 16 \({}^{\circ}\)C), which is a hallmark of ribosome biogenesis defects. The Hfq-deleted mutant accumulated free 30S subunits and the pre-16S rRNA; the 70S ribosome pool was reduced [122]. In addition, in this mutant strain, translation efficiency and fidelity were impaired: an increased frequency of frame shift, translation initiation on alternative start codons, and premature translation termination were observed.  
It was shown that trans expression of the recombinant Hfq suppressed the defects of the 30S subunit maturation. Analysis of Hfq protein mutants revealed that only one of the three RNA-binding sites is critical for ribosome biogenesis: mutations of the distal face of Hfq led to altered ribosomal profiles [106]. These profiles were similar to that of the _hfq_ null mutant. It was demonstrated that Hfq interacted with the 5\({}^{\prime}\)- and 3\({}^{\prime}\)-regions of the 17S rRNA [122]. In addition, Hfq and RNase R can form a complex, and cosediment with 30S subunits [123]. Double inactivation of the Hfq and RNase R genes (\(\Delta\)_hfq_\(\Delta\)_rrr_ mutant) led to notable cell growth defects and more substantial accumulation of unprocessed rRNAs compared to the \(\Delta\)_hfq_ mutant. These results indicated that RNase R interacts functionally with Hfq in the ribosome biogenesis. RNase R is highly effective against structured RNAs [124]. Cooperation between Hfq and RNase R may help eliminate RNA secondary structures and make the 5\({}^{\prime}\)- and 3\({}^{\prime}\)-ends available for folding, promoting the correct processing of 17S rRNA. Moreover, it has been reported that Hfq and RNAse R can associate with the ribosomal protein S12, which affects translation fidelity and is located close to the decoding center [125]. These findings indicated that Hfq and RNase R could interact with the pre-30S subunit through S12 and form the productive structure of the 17S rRNA 5\({}^{\prime}\)- and 3\({}^{\prime}\)-sequences, which are part of the decoding center.