A NEW FAMILY OF PLASMA-MEMBRANE POLYPEPTIDES DIFFERENTIALLY REGULATEDDURING PLANT DEVELOPMENT

Two cDNAs encoding polypeptides identified in a tobacco leaf plasma me mbrane fraction prepared by phase partitioning were cloned. The deduce d polypeptides, P16 and P17, exhibit a striking primary structure, sim ilar to that of P19, a previously cloned plasma membrane polypeptide. Antibodies raised to the recombinant proteins were used to probe the c ellular location of P16, P17 and P19 by means of western blotting of s ucrose density-gradient fractions; all three polypeptides were found t o be located solely at the plasma membrane. Furthermore, P19 antigen a ccumulated transiently at the time of floral induction while P16 and P 17 antigens accumulated towards the end of the life-cycle. These resul ts together with sequence database searches and multiple-sequence alig nments suggest that we have identified a new family of plasma membrane polypeptides that (i) are putatively plant specific and (ii) are diff erentially regulated during plant development. These polypeptides al-e termed DREPPs for developmentally regulated plasma membrane polypepti des.