Tcra-J^tm5Krg

A transcriptional terminator element and a frt-flnked neomycin cassette replaced an equivalent amount of genomic DNA downstream of the Tcra-J 56 element. The transcriptional terminator included four polyadenylation sites and 12 lac operators. The operator array was assembled as a tetramer of lac operator trimers with each trimer containing three copies of the sequence TGTGGAATTGTGAGCGCTCACAATTCCACA. Chimeric mice were bred with FLP recombinase mice to remove the neomycin cassette. Germline transcription of the downstream Tcra-J gene segments was reduced to less than 5% of controls in double positive thymocytes isolated from homozygotes on a Rag-null background. This allele differs from the Tcra-Jtm4Krg (56R) allele in that the terminator was inserted with no loss of genomic sequence: in the other (56R), the terminator replaced a genomic DNA segment of equal length. (J:147326)