The Prevotella loescheii adhesin gene, plaA, contains a coding gap between a small open reading frame (ORF-I) and a large open reading frame (ORF-2). Translation of the plaA mRNA requires bypassing this 29-nt coding gap on the plaA transcript. We have determined the N-terminal peptide sequence of the SO34 adhesin beyond the gap sequence. This sequence shows that the peptide junction between ORF-1 and ORF-2 is continuous in the adhesin and supports the conclusion that synthesis of the SO34 adhesin occurs by a ribosomal hop mechanism. To elucidate upstream signals, we used the 5' RACE (rapid amplification of cDNA ends) technique to map the start point of the plaA mRNA. DNA sequencing of plasmids with the 5' RACE products placed the 5' end of plaA mRNA 270 nt upstream from the plaA start codon. A region corresponding to a Bacteroides fragilis promoter consensus sequence precedes this start site.