Heterogeneous nuclear ribonucleoprotein complexes from Xenopus laevis oocytes and somatic cells

HnRNP proteins have been implicated in most stages of cellular mRNA metabol ism, including processing, nucleocytoplasmic transport, stability, and loca lization. Several hnRNP proteins are also known to participate in key early developmental decisions. In order to facilitate functional studies of thes e pre-mRNA- and mRNA-binding proteins in a vertebrate organism amenable to developmental studies and experimental manipulation, we identified and puri fied the major hnRNP proteins and isolated the hnRNP complex from Xenopus l aevis oocytes and somatic cells. Using affinity chromatography and immunolo gical methods, we isolated a family of >15 abundant single-stranded nucleic acid-binding proteins, which range in apparent molecular weight from simil ar to 20 kDa to >150 kDa, and with isoelectric points from <5 to >8. Monocl onal antibodies revealed that a subset of these proteins are major hnRNP pr oteins in both oocytes and somatic cells in culture, and include proteins r elated to human hnRNP A2/B1/B2 and hnRNP K. UV crosslinking in living cells demonstrated that these proteins bind poly(A)(+) RNA in vivo. Immunopurifi cation using a monoclonal antibody to X. laevis hnRNP A2 resulted in the is olation of RNP complexes that contain a specific subset of single-stranded nucleic acid-binding proteins. The protein composition of complexes isolate d from somatic cells and from oocyte germinal vesicles was similar, suggest ing that the overall properties and functions of hnRNP proteins in these tw o cell types are comparable. These findings, together with the novel probes generated here, will also facilitate studies of the function of vertebrate RNA-binding proteins using the well characterized X. laevis oocyte and ear ly embryo as experimental systems.