A CDNA CLONE FROM THE SEA LAMPREY PETROMYZON-MARINUS CODING FOR A SCAVENGER RECEPTOR CYS-RICH (SRCR) DOMAIN PROTEIN

Our knowledge of the immune system in the early vertebrates, the Agnat ha, and the molecules involved in their immune reactions is fragmentar y. By serendipity we discovered a cDNA clone in a library made from gu t poly(A)(+)RNA of the sea lamprey, Petromyzon marinus (Pema): that tr anslates into the SREG (SRCR-EGF, see below) protein which resembles c ell-membrane proteins of mammalian immune cells. The putative translat ed product is a type-I integral membrane glycoprotein which contains t wo scavenger receptor Cys-rich (SRCR) domains flanking five epidermal growth factor (EGF)-like repeats. The two SRCR domains are closely rel ated to CD6 (expressed on human lymphocytes), WC1 (expressed on mammal ian CD4(-)CD8(-)-gamma delta T cells) and M130 (expressed on human mac rophages). The Pema-SREG may therefore be involved in intercellular co ntacts and cell activation or differentiation in the immune system. It is thus a potential marker that can be used to investigate the lampre y immune system.