Ribosomal protein S7: a new RNA-binding motif with structural similarities to a DNA architectural factor.
BACKGROUND
The ribosome is a ribonucleoprotein complex which performs the crucial function of protein biosynthesis. Its role is to decode mRNAs within the cell and to synthesize the corresponding proteins. Ribosomal protein S7 is located at the head of the small (30S) subunit of the ribosome and faces into the decoding centre. S7 is one of the primary 16S rRNA-binding proteins responsible for initiating the assembly of the head of the 30S subunit. In addition, S7 has been shown to be the major protein component to cross-link with tRNA molecules bound at both the aminoacyl-tRNA (A) and peptidyl-tRNA (P) sites of the ribosome. The ribosomal protein S7 clearly plays an important role in ribosome function. It was hoped that an atomic-resolution structure of this protein would aid our understanding of ribosomal mechanisms.


RESULTS
The structure of ribosomal protein S7 from Bacillus stearothermophilus has been solved at 2.5 A resolution using multiwavelength anomalous diffraction and selenomethionyl-substituted proteins. The molecule consists of a helical hydrophobic core domain and a beta-ribbon arm extending from the hydrophobic core. The helical core domain is composed of a pair of entangled helix-turn-helix motifs; the fold of the core is similar to that of a DNA architectural factor. Highly conserved basic and aromatic residues are clustered on one face of the S7 molecule and create a 16S rRNA contact surface.


CONCLUSIONS
The molecular structure of S7, together with the results of previous cross-linking experiments, suggest how this ribosomal protein binds to the 3' major domain of 16S rRNA and mediates the folding of 16S rRNA to create the ribosome decoding centre.
Hosaka
H
H
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
Nakagawa
A
A
Tanaka
I
I
Harada
N
N
Sano
K
K
Kimura
M
M
Yao
M
M
Wakatsuki
S
S
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D001411:Geobacillus stearothermophilus / Q000737:chemistry*; D019077:Helix-Turn-Helix Motifs; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012335:RNA, Ribosomal / Q000737:chemistry / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry*; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; C040330:histone-like protein HU, bacteria; C037442:ribosomal protein S7