This mutation, discovered in a screen of G3 progeny of an ENU mutagenized mouse for susceptibility to infection by mouse cytomegalovirus (MCMV), comprises a G to A transversion at nucleotide position 33572 of the genomic sequence (GenBank genomic region NC_000072 for linear genomic sequence of Flt3). This destroys the donor splice site of intron 9, resulting in the use of an alternative donor splice site six nucleotides away, within exon 9, and thus causing deletion of the last two amino acids (tyrosine and serine) encoded by exon 9. (J:88776, J:159599)