function determines the identity of PSIO to PS13, 
and 2) the regulatory function suppresses the activ- 
ities of other homeotic genes in PS 14. Transcrip- 
tional analysis of Abd-B has revealed four overlap- 
ping transcripts that are generated from the Abd-B 
region. All four transcripts contain a unique 5' 
exon but share several 3' exons. Promoters for two 
of the transcripts (4.6 and 3 4 kb) have been identi- 
fied. The 4.6 kb RNA initiates —25 kb downstream 
of the 3.4 kb RNA initiation site. Two other tran- 
scripts initiate farther upstream of these promoters. 
Although the Abd-B transcripts initiate from multi- 
ple promoters, they are polyadenylated at the same 
two sites. DNA sequence analysis of the Abd-B 
cDNAs indicates that the 4.6 kb RNA encodes a 55 
kDa protein; a 30 kDa protein is produced by three 
other transcripts. Both proteins contain a homeo- 
domain, but they differ by the presence or absence 
of a 25 kDa domain on the amino terminus. In situ 
hybridization and immunofluorescence techniques 
are being used to localize RNA and protein prod- 
ucts in both the wild-type and mutant Drosophila 
embryos. The results support the assignment of the 
morphogenetic function (active in PS 10-13) to the 
55 kDa protein and the regulatory function (active 
in PS 14) to the 30 kDa protein. 
Dr. Sakonju is also Assistant Professor of Human 
Genetics at the University of Utah School of Medi- 
cine. 
288 
