No abstract

The human PAX3 gene contains a paired box and a paired-type homeobox, and is believed to play a role in pattern formation in the embryo. We describe the exon-intron structure of the homeobox-containing part of PAX3, complementing earlier descriptions of the 5' part of the gene. Mutations in PAX3 have been described in patients with Type 1 Waardenburg syndrome, who have hearing loss and pigmentary abnormalities, while Splotch mice have mutations in the homologous mouse Pax-3 gene. We describe a series of patients who have previously unidentified PAX3 mutations. These include a chromosomal deletion, a splice-site mutation and an amino acid substitution which closely correspond to the molecular changes seen in the Splotch-retarded, Splotch and Splotch-delayed mouse mutants respectively. These mutations confirm that Waardenburg syndrome is produced by gene dosage effects and show that the phenotypic differences between Splotch mice and humans with Waardenburg syndrome are caused by differences in genetic background rather than different primary effects of the mutations.

The grain hardness locus, Ha, is located at the distal end of the short arm of chromosome 5D in wheat. Three polypeptides, puroindoline-a, puroindoline-b, and grain softness protein (GSP-1), have been identified as components of friabilin, a biochemical marker for grain softness, and the genes for these polypeptides are known to be tightly linked to the Ha locus. However, this region of the chromosome 5D has not been well characterized and the physical distance between the markers is not known. Separate lambda clones containing the puroindoline-a gene and the puroindoline-b gene have been isolated from an Aegilops tauschii (the donor of the D genome to wheat) genomic lambda library and investigated. Considerable variation appears to exist in the organization of the region upstream of the gene for puroindoline-b among species closely related to wheat. Using in situ hybridization the genes for puroindoline-a, -b, and GSP-1 were demonstrated to be physically located at the tip of the short arm of chromosome 5 of A. tauschii. Four overlapping clones were isolated from a large-insert BAC library constructed from A. tauschii and of these one contained genes for all of puroindoline-a, puroindoline-b, and GSP-1. The gene for puroindoline-a is located between the other two genes at a distance no greater than approximately 30 kb from either gene. The BAC clone containing all three known genes was used to screen a cDNA library constructed from hexaploid wheat and cDNAs that could encode novel polypeptides were isolated.