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

Abstract

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