Using ES cells in which a correctly targeted modification of the Sftpa gene had already been created, exon 2 along with the translation start site, was replaced with a PGK-neomycin cassette. Northern blot analysis demonstrated the absence of any Sftpa mRNA in any doubly homozygous mice as well as the absence of full length Sftpd mRNA. A small amount of truncated mRNA for Sftpd lacking the translation start site was seen. Western blot analysis confirmed that no protein products were produced.