These are heterogeneous mixtures of proteins comprising subunits linked by disulphide bonds. 'A' are high-molecular-weight (HMW) and 'B', 'C', and 'D' are low-molecular-weight (LMW) subunits. The Glu loci, all of which are compound, encode HMW glutenin subunits.
Each Glu-1 locus in hexaploid wheat contains two genes, the products of which were described as 'x-type' and 'y-type' based on differences in molecular weight and isoelectric point (738). Other evidence has shown these gene products to differ in electrophoretic finger print pattern (739) and cysteine content (747), and the genes themselves to differ in nucleotide sequence (740, 741, 742). Although early evidence suggested up to 6 genes in total at each locus (744, 742) it appears likely that only a single copy of each gene is present at the 1AL, 1BL, and 1DL loci (743).
No 'y-type' protein from the Glu-A1 locus has been demonstrated in hexaploid wheat (738) and sequencing experiments have shown the presence of a terminating sequence inside the transcribed portion of the gene (742). The gene coding for 'x-type' proteins within Glu-A1 is also often silent (738, 641).
The symbols for the genes within the Glu-1 loci coding for x-type and y-type proteins will be Glu-1-1 and Glu-1-2, respectively, rather than Glu-1x and Glu-1y (740). The genes are closely linked but recombination has been observed between Glu-B1-1 and Glu-B1-2 with a frequency of 3 in 3450 (668). The gene order, relative to the centromere, has not been ascertained.
Although alleles at each gene within the Glu-1 compound loci could reasonably be named, the system of naming alleles on the combinations of Glu-1-1 and Glu-1-2 products has been retained in this edition.
