The dzrl locus in maize posttranscriptionally regulates the accumulation of methionine-rich 10 kDa zein in the endosperm. An allele of this locus present in the inbred line BSSS53, dzrl + BSSS53, conditions several-fold higher accumulation of the 10 kDa zein in comparison with standard inbred lines, leading to enrichment of methionine content in BSSS53 by 30%. In a population segregating for high and low 10 kDa zein, dzr1 + BSSS53 was found tightly to cosegregate with a 22 kDa zein gene cluster, belonging to the Z1C subfamily of alpha-zeins that is located on chromosome 4S. One member of this gene cluster, azs22/6, was estimated to be located less than 0.4 cM from dzr1 + BSSS53, while three other 22 kDa zein genes mapped 3.4 cM away. Restriction fragment length polymorphism (RFLP) mapping of dzr1 was conducted using additional maize DNA markers and orthologous rice DNA markers. One maize marker, php20725, was identified that mapped 1.1 cM from dzr1, proximal to the centromere. Another marker derived from rice, rz329, mapped 6.6 cM distal to dzr1. Pulsed-field gel electrophoresis (PFGE) of the 22 kDa zein cluster showed that probably all copies of the 22 kDa zein genes are present within a 200 kb SalI fragment. The recombination frequency within this cluster was estimated to be 20-fold higher than that predicted for the maize genome.