Nomenclature for isozyme genes in maize
Formal genetic analyses have been reported for a number of maize isozymes over the past decade. Many isozyme systems have both multiple loci and multiple alleles. Since there has existed some confusion in the literature as to the proper conventions for nomenclature of isozyme genes and alleles, we describe below a few simple rules which should help clarify this situation. We also present here a list of the maize isozyme genes which have been studied in our laboratory. Only those isozymes which have been defined genetically are listed in Table I. Not included, therefore, are isozyme bands for which electrophoretic variants have not been found or for which formal genetic analysis has not yet been determined.
The references listed in Table I are those which define the isozyme system in terms of gel patterns, developmental and/or biochemical data. The abbreviation for maize catalase genes has been changed from Ct to Cat in order to avoid confusion with the older designation of clumped tassel as Ct. We have also changed the designation of maize aminopeptidase genes from Lap (leucine aminopeptidase) to Amp in order to reflect overlapping specificities toward amino acid-naphthylamides.
To conform with the adopted rules of nomenclature for defining maize genes we are adhering to the following system and suggest it for other isozyme genes. Preferably a three-letter abbreviation for the isozyme gene is used and is followed by the locus number. Both letter and number are italicized, the first letter being capitalized. When designating a particular allele, the gene symbol is followed by a dash and the allelic symbol (also italicized), which is usually a reference to the electrophoretic mobility of the isozyme gene product. For example, the Cat1-F allele codes for the catalase subunit CAT-1F.
Either a letter or a number can be used to denote the allelic isozyme products under a given set of electrophoretic conditions. Designating the band positions of a multi-locus isozyme system is also a matter of choice with the only rule which should be strictly adhered to being that the first genetically-defined isozyme locus to be reported is given the numerical designation 1, the second 2, etc., regardless of the isozyme band number which corresponds to the gene product. For example, Mdh2 has two alleles, Mdh2-m3 and mdh2-m5, which code for mitochondrial malate dehydrogenase isozymes mMDH-3 and mMDH-5, respectively.
Flexibility is allowed in the allelic designation in order to encompass differing degrees of complexity of the isozyme system. For isozymes which show distinct subcellular compartmentations, it is often useful to maintain this information in the allelic symbol by using m, g, s, or c for mitochondrial, glyoxysomal, soluble, or chloroplast.
Unfortunately, very few isozyme genes have been mapped to date. We are presently attempting to localize a number of the genes listed in Table I in order to extend their usefulness as biochemical-genetic markers.
Lila A. Ott and John G. Scandalios
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