The Sm domain is an ancient RNA-binding motif with oligo(U) specificity.
Sm and Sm-like proteins are members of a family of small proteins that is widespread throughout eukaryotic kingdoms. These proteins form heteromers with one another and bind, as heteromeric complexes, to various RNAs, recognizing primarily short U-rich stretches. Interestingly, completion of several genome projects revealed that archaea also contain genes that may encode Sm-like proteins. Herein, we studied the properties of one Sm-like protein derived from the archaebacterium Archaeoglobus fulgidus and overexpressed in Escherichia coli. This single small protein closely reflects the properties of an Sm or Sm-like protein heteromer. It binds to RNA with a high specificity for oligo(U), and assembles onto the RNA to form a complex that exhibits, as judged by electron microscopy, a ring-like structure similar to the ones observed with the Sm core ribonucleoprotein and the like Sm (LSm) protein heteromer. Importantly, multivariate statistical analysis of negative-stain electron-microscopic images revealed a sevenfold symmetry for the observed ring structure, indicating that the proteins form a homoheptamer. These results support the structural model of the Sm proteins derived from crystallographic studies on Sm heterodimers and demonstrate that the Sm protein family evolved from a single ancestor that was present before the eukaryotic and archaeal kingdoms separated.
Max Planck Institute of Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
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D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019611:Archaeoglobus fulgidus / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009843:Oligoribonucleotides / Q000737:chemistry / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D014500:Uracil Nucleotides / Q000737:chemistry / Q000378:metabolism*
D008565:Membrane Proteins; D009843:Oligoribonucleotides; D010750:Phosphoproteins; D017411:Ribonucleoproteins, Small Nuclear; C090865:Sm protein D2; D014500:Uracil Nucleotides; C027916:oligo(U)