Protein-protein and protein-RNA contacts both contribute to the 15.5K-mediated assembly of the U4/U6 snRNP and the box C/D snoRNPs.
The k-turn-binding protein 15.5K is unique in that it is essential for the hierarchical assembly of three RNP complexes distinct in both composition and function, namely, the U4/U6 snRNP, the box C/D snoRNP, and the RNP complex assembled on the U3 box B/C motif. 15.5K interacts with the cognate RNAs via an induced fit mechanism, which results in the folding of the surrounding RNA to create a binding site(s) for the RNP-specific proteins. However, it is possible that 15.5K also mediates RNP formation via protein-protein interactions with the complex-specific proteins. To investigate this possibility, we created a series of 15.5K mutations in which the surface properties of the protein had been changed. We assessed their ability to support the formation of the three distinct RNP complexes and found that the formation of each RNP requires a distinct set of regions on the surface of 15.5K. This implies that protein-protein contacts are essential for RNP formation in each complex. Further supporting this idea, direct protein-protein interaction could be observed between hU3-55K and 15.5K. In conclusion, our data suggest that the formation of each RNP involves the direct recognition of specific elements in both 15.5K protein and the specific RNA.
Schultz
Annemarie
A
Max Planck Institute of Biophysical Chemistry, Am Fassberg 11, D-37070 Göttingen, Germany.
Nottrott
Stephanie
S
Watkins
Nicholas James
NJ
Lührmann
Reinhard
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D025941:Protein Interaction Mapping; D017433:Protein Structure, Secondary; D012313:RNA / Q000737:chemistry; D020537:RNA, Small Nucleolar / Q000737:chemistry; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry*; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry* / Q000235:genetics; D020718:Ribonucleoproteins, Small Nucleolar / Q000737:chemistry*
D020537:RNA, Small Nucleolar; C117378:RNA, U3 small nucleolar; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D020718:Ribonucleoproteins, Small Nucleolar; C402291:Snu13 protein, human; D012313:RNA