AbstractThe VpreBgenes, which encode surrogate immunoglobulin light chain molecules, are expressed as RNA almost exclusively in pre‐B cells. We have investigated the transcriptional control mechanisms which are responsible for the pre‐B cell‐specific RNA expression of the mouse VpreB1and VpreB2genes. Nuclear run‐on analyses demonstrate that the pre‐B cell‐specific expression of both VpreBgenes is controlled primarily at the level of initiation of transcription. S1 nuclease protection‐mapping defined two or three major start sites of transcription for the VpreBgenes. To find a promoter and other potential cis‐acting regulatory elements, a 700‐bp fragment 5′ of the transcription start sites of the VpreB1gene was used in gene transfer experiments and found to act as a promoter in pre‐B lymphocytes. Deletion experiments showed that 191 bp upstream of the most 5′ transcription start site is required for the pre‐B cell promoter activity. DNA sequence analysis of the 5′ region of the mouse VpreB1, VpreB2and human VpreBgenes reveal that this region of approximately 200 bp is strongly conserved. This 200‐bp promoter region contains several conserved nucleotide sequence motifs which may act to mediate the pre‐B cell‐specifi