CDNA STRUCTURE, EXPRESSION AND NUCLEIC ACID-BINDING PROPERTIES OF 3 RNA-BINDING PROTEINS IN TOBACCO - OCCURRENCE OF TISSUE-SPECIFIC ALTERNATIVE SPLICING

Three cDNAs encoding RNA-binding proteins were isolated from a tobacco (Nicotiana sylvestris) cDNA library. The predicted proteins (RGP-1) a re homologous to each other and consist of a consensus-sequence type R NA-binding domain of 80 amino acids in the N-terminal half and a glyci ne-rich domain of 61-78 amino acids in the C-terminal half. Nucleic ac id-binding assay using the in vitro synthesized RGP-1 protein confirme d that it is an RNA-binding protein. Based on its strong affinity for poly(G) and poly(U), the RGP-1 proteins are suggested to bind specific ally to G and/or U rich sequences. All three genes are expressed in le aves, roots, flowers and cultured cells, however, the substantial amou nt of pre-mRNAs are accumulated especially in roots. Sequence analysis and ribonuclease protection assay indicated that significant amounts of alternatively spliced mRNAs, which are produced by differential sel ection of 5' splice sites, are also present in various tissues. Tissue -specific alternative splicing was found in two of the three genes. Th e alternatively spliced mRNAs are also detected in polysomal fractions and are suggested to produce truncated polypeptides. A possible role of this alternative splicing is discussed.