The chromosomal gene encoding human aldolase B was isolated. The gene is composed of nine exons interrupted by eight introns and spans 15 kb, and a single copy of it occurs per haploid human genome. The initiation of transcription occurs at three different sites. Two minor sites, m1 and m2, start at 49 and 21 nucleotides, respectively, upstream from the major site, M. The gene also carries poly(A) addition signals at two different sites, thereby another two distinct mRNA species are produced. We examined the sequences required for mRNA 3'-end formation in this gene carrying multiple poly(A) addition sites. By constructing deletion mutants as to the region distal to the poly(A) addition site and then assaying through transfection into COS-1 cells, we demonstrated that 8 nucleotides distal to the site of poly(A) addition is sufficient for proximal polyadenylation, but is not sufficient for distal polyadenylation.