A novel germ-line JK transcript starting immediately upstream of JK1.

Germ-line transcripts of the immunoglobulin (Ig) and T cell receptor loci are thought to be involved in the control of V gene rearrangement by rendering these loci accessible to the recombinases. We have analyzed the transcriptional activity of germ-line K alleles in two bone marrow-derived Abelson-murine leukemia virus transformed pre-B cells: 300-19, a null cell line, and P8 a mu-producing line. We found a novel germ-line JK transcript starting immediately upstream of JK1 and spliced to CK. The potential role of this transcript in the opening of the Ig K locus as well as in the ordered usage of JK segments is discussed.