Two novel exons, named exon 1A and exon 2A, were found at 18.4 and 12.6 kb upstream from the exon known as the first exon of human Fc is an element of RI alpha -chain gene. Transcription from the promoter present in the upstream of exon 1A was decreased by mutations introduced into the "first intron" between exon IA and exon 2A, suggesting the presence of an intronic regulatory element in the intron. Consistent with this, electrophoretic mobility shift assay revealed the presence of a nuclear factor which bound the region in Fc is an element of RI alpha -chain positive cells.