Estimation of the number of genes specifying the heavy chain of mouse thymus leukemia antigens.

We have investigated the number of structural genes present in ASL-1 cells, a murine leukemia cell line which encodes the heavy chain of thymus leukemia (TL) antigens, a protein which is similar to the Class I histocompatibility antigens. TL-specific messenger RNA was purified from polysomes of ASL-1 cells by immunoprecipitation, and this messenger RNA translated in vitro to produce a Mr 42,000 protein which comigrated on acrylamide gel with nonglycosylated TL heavy chain. A 32P-labeled complementary DNA (cDNA) was synthesized by reverse transcription of the TL-specific messenger RNA as template. Analysis of reassociation kinetics of the 32P-TL-cDNA with DNA from ASL-1 cells showed that the kinetics was indistinguishable from that obtained using a DNA encoding a single-copy gene (C mu). An analysis was performed in which DNA from ASL-1 cells was subjected to digestion with each of three restriction enzymes and hybridized with 32P-TL-cDNA according to the Southern "blot" technique. Two bands formed hybrids with the 32P-TL-cDNA with each of three restriction enzymes used. These data are consistent with the presence of a small number of structural genes for the TL heavy chain in the genome of ASL-1 leukemia cells.