The recovery of a B2 insertion in the lacI gene of a rat cell line containing a lambda/LIZ shuttle vector

The bacterial lacl gene is in use as a reporter gene for mutation in transgenic mice, rats and in cell lines. During a mutagenesis study in which we used such a rat cell line, we recovered a mutant which features an insertion of a rat B2 repeated sequence element. This sequence element was inserted between positions 77 and 78 in the lad gene. When the inserted sequence was compared to the published rat B2 sequences, two short deletions, possibly mediated by short repeat sequences, were revealed. This is the first demonstration of the recovery of a repeated sequence element into the lacl gene used in transgenic animals and cell lines, and confirms previous findings that such sequences indeed move around the genome.