CELL-SURFACE EXPRESSION OF THE SHORT IMMUNOGLOBULIN MU CHAIN (D-MU PROTEIN) IN MURINE PRE-B-CELLS IS DIFFERENTLY REGULATED FROM THAT OF THE INTACT MU CHAIN

Pre-B cells carrying DJ(H) rearrangements in an appropriate reading frame produce a short mu-protein consisting of a DJ(H) and the C-mu-& sequence (D-mu-protein). We analyzed a D-mu-producing Abelson-murine leukemia virus-transformed murine pre-B line, 300-19, and demonstrated that D-mu-proteins are expressed on the cell surface in association with surrogate L chain proteins (lambda-5 and V(preB)). However, when we introduced an expression vector coding for the D-mu-protein into the null pre-B line P17-27, which produce lambda-5 and V(preB) but no Ig molecules, most of the cells did not express D-mu-proteins on the cell surface although D-mu-proteins were produced intracellularly. On the other hand, P17-27 brings intact-mu-chains on the cell surface, when a vector coding for the intact-mu-chain is introduced. Thus, cell surface expression of the D-mu-protein has different requirements from that of the intact-mu-chain. A possible role of the V(H) protein encoded by germ-line V(H) transcripts is discussed.