Research Papers

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 cellline, RC-kappa 8;Drosophila ME31 B, encoded by amaternally-expressed gene, and Saccharomyces pombe Ste13, cloned by complementation of the sterility mutant stela 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.