Résumé
A rare mRNA variant of the human lymphocyte-specific protein tyrosine kinase
LCK gene that retains intron B and excludes exon 7 (B
+7
−) due to alternative splicing of the canonical LCK transcripts was identified and characterized. LCK B
+7
− mRNA is detected in all tested peripheral blood T lymphocytes total RNA samples but is apparently sequestered in the nucleus. The presence of intron B sequence does not disrupt the reading frame and results in the insertion of 58 aminoacids, containing a proline-rich region just upstream of p56lck SH3 domain. This putative isoform encodes an unstable 516 aminoacids protein (Lck
B+7−) which can be expressed in transfected COS-7 cells. Furthermore in Jurkat T cell extracts, a recombinant intron B plus SH3 p56lck domain fails to interact with some TCR-induced tyrosine phosphorylated polypeptides and known p56lck partners such as Sam68 and
c-Cbl. The biological function of this rare messenger remains to be elucidated.