SEQUENCES REQUIRED FOR PARAMUTATION OF THE MAIZE B-GENE MAP TO A REGION CONTAINING THE PROMOTER AND UPSTREAM SEQUENCES

The b gene encodes a transcriptional regulator of the maize anthocyani n biosynthetic pathway. Certain b alleles participate in paramutation, an allele-specific interaction that heritably alters transcription. T he moderately transcribed B' allele heritably reduces the transcriptio n of the highly transcribed B-I allele in a B'/B-I heterozygote, such that the B-I allele becomes B'. To identify the cis-acting sequences r equired for paramutation, we used B' or B-I alleles to isolate intrage nic recombinants with B-Peru, an allele that is insensitive to paramut ation and has distinct tissue-specific regulation. Physical mapping of the recombinant aneles showed that most of the crossovers were in a s mall region near the 5' end of the b-transcribed region. Analysis of t he recombinant alleles revealed that the ability to cause and respond to paramutation and the control of tissue-specific expression both loc alize to the 5' region of the gene. The 3' boundary of these functions lies just upstream of the translation initiation codon. The 5' bounda ry has been estimated to be no more than 0.1 cM further upstream (1-15 0 kb). Thus, sequences critical for paramutation lie upstream of the b coding sequences and may include transcriptional regulatory sequences .