Structure and mechanism of a molecular rheostat, an RNA thermometer that modulates immune evasion by Neisseria meningitidis.

Neisseria meningitidis causes bacterial meningitis and septicemia. It evades the host complement system by upregulating expression of immune evasion factors in response to changes in temperature. RNA thermometers within mRNAs control expression of bacterial immune evasion factors, including CssA, in the 5'-untranslated region of the operon for capsule biosynthesis.

The box H/ACA snoRNP assembly factor Shq1p is a chaperone protein homologous to Hsp90 cochaperones that binds to the Cbf5p enzyme.

Box H/ACA small nucleolar (sno) ribonucleoproteins (RNPs) are responsible for the formation of pseudouridine in a variety of RNAs and are essential for ribosome biogenesis, modification of spliceosomal RNAs, and telomerase stability. A mature snoRNP has been reconstituted in vitro and is composed of a single RNA and four proteins. However, snoRNP biogenesis in vivo requires multiple factors to coordinate a complex and poorly understood assembly and maturation process.

How arginine-rich domains coordinate mRNA maturation events.

Maturation of RNA is highly regulated from transcription to post-transcriptional processing and localization to specific cellular compartments. The complexes that contribute to these events are in many cases well understood; however, many of the protein factors that coordinate and regulate these RNA processing events remain poorly characterized. Among them are arginine-rich domains, most commonly sequences rich in arginine/serine (RS domains) or arginine/glycine/glycine (RGG boxes), that often appear among factors and complexes involved in RNA processing.

The box H/ACA RNP assembly factor Naf1p contains a domain homologous to Gar1p mediating its interaction with Cbf5p.

Naf1 is an essential protein involved in the maturation of box H/ACA ribonucleoproteins, a group of particles required for ribosome biogenesis, modification of spliceosomal small nuclear RNAs and telomere synthesis. Naf1 participates in the assembly of the RNP at transcription sites and in the nuclear trafficking of the complex. The crystal structure of a domain of yeast Naf1p, Naf1Delta1p, reveals a striking structural homology with the core domain of archaeal Gar1, an essential protein component of the mature RNP; it suggests that Naf1p and Gar1p have a common binding site on the enzymatic protein component of the particle, Cbf5p.

A new alpha-helical extension promotes RNA binding by the dsRBD of Rnt1p RNAse III.

Rnt1 endoribonuclease, the yeast homolog of RNAse III, plays an important role in the maturation of a diverse set of RNAs. The enzymatic activity requires a conserved catalytic domain, while RNA binding requires the double-stranded RNA-binding domain (dsRBD) at the C-terminus of the protein. While bacterial RNAse III enzymes cleave double-stranded RNA, Rnt1p specifically cleaves RNAs that possess short irregular stem-loops containing 12-14 base pairs interrupted by internal loops and bulges and capped by conserved AGNN tetraloops.