title: Xp54, the Xenopus homologue of human RNA helicase p54, is an integral component of stored mRNP particles in oocytes.
abstract: In investigating the composition of stored (maternal) mRNP particles in Xenopus oocytes, attention has focussed primarily on the phosphoproteins pp60/56, which are Y-box proteins involved in a general packaging of mRNA. We now identify a third, abundant, integral component of stored mRNP particles, Xp54, which belongs to the family of DEAD-box RNA helicases. Xp54 was first detected by its ability to photocrosslink ATP. Subsequent sequence analysis identifies Xp54 as a member of a helicase subfamily which includes: human p54, encoded at a chromosomal breakpoint in the B-cell lymphoma cell line, RC-K8; Drosophila ME31B, encoded by a maternally-expressed gene, and Saccharomyces pombe Ste13, cloned by complementation of the sterility mutant ste13. Expression studies reveal that the gene encoding Xp54 is transcribed maximally at early oogenesis: no transcripts are detected in adult tissues, other than ovary. Using a monospecific antibody raised against native Xp54, its presence in mRNP particles is confirmed by immunoblotting fractions bound to oligo(dT)-cellulose and separated by rate sedimentation and buoyant density. On isolating Xp54 from mRNP particles, it is shown to possess an ATP-dependent RNA helicase activity. Possible functions of Xp54 are discussed in relation to the assembly and utilization of mRNP particles.
authors.affiliation: School of Biological and Medical Sciences, Bute Buildings, University of St Andrews, St Andrews, Fife KY16 9TS, UK.
authors.forename: M
authors.initials: M
authors.lastname: Ladomery
authors.forename: E
authors.initials: E
authors.lastname: Wade
authors.forename: J
authors.initials: J
authors.lastname: Sommerville
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000201:enzymology*; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases / Q000032:analysis / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D012261:Ribonucleoproteins / Q000737:chemistry*; D014982:Xenopus laevis
chemical_list: D018076:DNA, Complementary; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D012316:RNA Nucleotidyltransferases; D020365:RNA Helicases