title: Molecular cloning, characterization, and chromosomal localization of a human lymphoid tyrosine kinase related to murine Blk.
abstract: Triggering of Ag receptors on lymphocytes induces rapid phosphorylation of several receptor-associated protein tyrosine kinases (PTKs), implicating their role in controlling cellular growth and differentiation. In this study, we report the cloning of a human cDNA encoding a nonreceptor PTK with a calculated M(r) of about 58 kDa. The kinase has an overall amino acid identity of approximately 87% with the murine Blk. However, in the unique domain there is only 58% homology and an insertion of six amino acids in the N-terminal region. The nature of this insertion suggests a functional role in membrane attachment. Northern blot analysis showed expression in all stages of B cell development and in T cell lines. The message was not observed in the nonlymphoid tissues examined. In contrast, expression of murine blk in plasma cells and T lymphocytes has not been reported. Importantly, transcripts were seen in human embryonic liver as early as 7.5 wk of gestation before the rearrangement of Ig H chain locus. Furthermore, transcripts were detected in human thymocytes and not in mature T cells. Southern blot analysis revealed polymorphism of this gene in a Caucasian population but not in a Gambian population, indicating a recent origin of this polymorphism. The gene was localized to chromosome 8p22-23. The homology at the protein level suggests that this kinase may be the human homologue of murine Blk. Expression of BLK in immature T cells suggests that BLK may play an important role in thymopoiesis.
authors: Center for BioTechnology, Karolinska Institute, NOVUM, Huddinge, Sweden.
authors: K B
authors: KB
authors: Islam
authors: H
authors: H
authors: Rabbani
authors: C
authors: C
authors: Larsson
authors: R
authors: R
authors: Sanders
authors: C I
authors: CI
authors: Smith
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015139:Blotting, Southern; D002454:Cell Differentiation / Q000235:genetics; D002874:Chromosome Mapping / Q000379:methods; D003001:Cloning, Molecular; D015698:Genomic Library; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology; D017386:Sequence Homology, Amino Acid; D013601:T-Lymphocytes / Q000502:physiology; D014407:Tumor Cells, Cultured; D019061:src-Family Kinases
chemical_list: C082599:protein-tyrosine kinase p55(blk); D011505:Protein-Tyrosine Kinases; D019061:src-Family Kinases