Proline- and alanine-rich N-terminal extension of the basic bovine beta-crystallin B1 chains.

The amino acid sequence of the N-terminal region of the two basic bovine beta-crystallin B1 chains has been analyzed. The results reveal that beta B1b is derived in vivo from the primary gene product beta B1a by removal of a short N-terminal sequence. It appears that the beta B1 chains have the same domain structure as observed in other beta- and gamma-crystallin chains. They have, however, a very long N-terminal extension in comparison with other beta-chains. This extension is mainly composed of a remarkable Pro- and Ala-rich sequence, which suggests an interaction of these structural proteins with the cytoskeleton and/or the plasma membranes of the lens cells.