A chicken hnRNP of the A/B family recognizes the single-stranded d(CCCTAA)(n)telomeric repeated motif

With the aim of identifying proteins able to interact with the C-rich singl e-stranded telomeric repeated motif, three nuclear polypeptides, CBNP alpha CBNP beta and CBNP gamma, with apparent mobilities in SDS/PAGE of 38, 44 a nd 55 kDa, respectively, were isolated from mature chicken erythrocytes by affinity chromatography. In situ UV-cross-linking experiments demonstrated that CBNP alpha and CBNP gamma interact directly with the telomeric d(CCCTA A)(n) repeat, whereas CBNP beta does not. Moreover, they provided informati on on the protein components responsible for each electrophoretic mobility- shift assay signal. Ion spray and matrix-assisted laser desorption ionizati on MS allowed us to identify CBNP alpha with single-stranded D-box-binding factor (ssDBF), a protein previously characterized as a transcription facto r belonging to the A/B family of heterogeneous nuclear ribonucleoproteins, and CBNP beta with an isoform of this protein containing an extra exon. Sim ilarly, CBNP gamma was shown to be probably the chicken homolog of hnRNP K, a ribonuclear protein able to bind to polyC oligonucleotides. The relation of CBNP alpha (i.e. ssDBF), CBNP beta and CBNP gamma to a number of simila r proteins in the protein and nucleotide sequence databank is discussed. A rather diversified spectrum of functional roles has been assigned to some o f these proteins despite the strong sequence homology among them.