Molecular cloning of a novel N-terminal variant of annexin II from rat basophilic leukaemia cells.

Rat annexin II cDNA clones were isolated from a rat basophilic leukaemia cell plasmid library by cross-species hybridization with a mouse probe, and fully sequenced using the dideoxy-chain-termination method. Alignment of the derived amino-acid sequence with those of other mammalian annexin II species revealed a high level of conservation, characteristic of the annexin family of proteins. One of the cDNAs isolated contained an additional six nucleotides close to the N-terminus, lying in-frame and at a point corresponding to an intron/exon boundary in the human annexin II gene. As the two rat cDNAs were identical apart from the six nucleotide insert, it is likely that these represent alternatively spliced transcripts of a single gene, rather than the products of two separate genes. The six nucleotides encode serine-glutamine and therefore introduce an additional potential phosphorylation site into a region already containing one tyrosine and two serine phosphorylation sites. The discovery of this novel annexin II variant may have important implications both for p11 binding and for regulation of annexin II function by phosphorylation.