We have continued the studies which we reported last year (MNL 55:23, 1981). Using single and double digestion with various restriction enzymes, followed by Southern blotting against our sucrose synthase cDNA, cloned in pBR322, we have constructed a restriction map around our hybridizing region with wild type DNA and with the DNAs of mutants sh-m5933 and sh-m6233. This map is divided into two parts by a BglII cleavage site within our probe. It could be shown that the map on the side corresponding to the larger part of our probe (500bp) is identical in the strains used, while differences are observed on the other side. We ascribe these differences to the presence of Ds at the Sh locus.
A comparison of the cDNA clones isolated by Burr and Burr (Genetics 98:143, 1981), by us (Geiser et al., Nucl. Acids Res. 8:6175, 1980) and by N. Fedoroff (personal communication), shows a size increase in the direction from the larger to the smaller BglII fragment. This indicated that the 5' end of the mRNA encoded by the gene is located in that part of our map, where we see the differences between wild type and mutants.
As the mutants can revert to the Sh, they must contain the complete coding sequence. From the data published by B. McClintock, we consider the possibility that the mutations are caused by deletions extending from an insertion site of Ds, towards the shrunken gene. From the data discussed above, we would conclude that the endpoints of these deletions are located upstream from the gene, possibly in its regulatory region.
We have cloned a 19kb BamHI fragment from the wild type and a 21 kb BclI fragment from the sh-m5933 in l 1059 (Karn et al., Proc. Natl. Sci. USA 77:5172-5176, 1980). The restriction maps obtained coincide with those of the genomic DNA. We are presently trying to map the gene in the wild type DNA and to characterize the non-wild type DNA obtained from the mutant, which possibly contains part or all of Ds.
H. P. Doring, M. Geiser, E. Weck, U. Courage-Tebbe, E. Tillmann and P. Starlinger
Return to the MNL 56 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page