Cytogenetic distinction between the TK+ and TK- chromosomes in the L5178Y TK+/- 3.7.2C mouse-lymphoma cell line.

We have analyzed the banded metaphase karyotypes of the L5178Y TK+ / − 3.7.2C mouse-lymphoma cell line as well as a class of slow growing (σ) TK+ / − mutants which show chromosome 11 rearrangements. We have discovered a centromeric heteromorphism in the chromosomes 11 (the known location of the thymidine kinase gene in the mouse) which, together with the types of chromosome rearrangements thus far catalogued for TK+ / − → TK− / − mutagenesis, allows us to propose a cytogenetic distinction between the TK-competent (TK+) and TK-deficient (TK−) chromosome.