Molecular characterization of the major maize embryo globulin encoded by the glb1 gene

One of the most abundant proteins in maize (Zea mays L.) embryos is the molecular weight 63,000 globulin encoded by the Glb1 gene. To obtain DNA clones corresponding to Glb1, a cDNA library corresponding to RNA from developing maize embryos was constructed in a lambda expression vector and screened with antibodies specific for Glb1-encoded proteins. Here we report the complete nucleotide sequence, as determined from two overlapping clones, of pcGlb 1S, a 2009 base pair clone containing the entire translated region of Glb1. The deduced amino acid sequence of pcGlb 1S shows similarities to 7S-type seed storage proteins of wheat and legumes. Southern blot analysis of maize DNA confirms previous genetic studies which had indicated the presence of a single copy of Glb1 per haploid genome. Northern blot analysis indicates that Glb1 transcripts are present throughout most of embryo development and that expression of this gene is limited to seed tissues. Embryos homozygous for a Glb1 null allele, in which Glb1-encoded proteins are not detectable, contain low levels of Glb1 transcripts which are a different size from those encoded by functional alleles. This suggests that the defect in the null allele is at the level of gene transcription or RNA processing.