IDENTIFICATION OF POLYPEPTIDES WHOSE PRESENCE CORRELATES WITH RETENTION OR LOSS OF AN ALBUMIN EXTINGUISHER CHROMOSOME IN RAT HEPATOMA MOUSE L-CELL FIBROBLAST MICROCELL HYBRIDS

The total protein content of a series of hybrids derived from the fusion of rat hepatoma cells with microcells of mouse L cell fibroblasts has been evaluated by two-dimensional electrophoresis. The parental rat hepatoma cells express a large set of hepatic functions, including the production of albumin. In the microcell hybrids containing chromosome M1 (marker1) as the unique mouse chromosome, it has been previously shown that rat albumin production is selectively extinguished, and that this extinction is no longer observed when chromosome M1 is partially or completely lost. Our current results show that albumin-producing and -nonproducing microcell hybrids have very similar polypeptide patterns, although a few differences are detected and can be classified in coherent categories. One of these polypeptides is a fibroblast protein whose synthesis is maintained and strictly correlated with the albumin extinction phenotype. It thus represents a potential candidate for a negative regulator of albumin expression.