Regulation of the parathyroid hormone gene by vitamin D,late the PTH gene and these will be considered in the calcium, and phosphate. Secondary hyperparathyroidism is a present review. frequent complication of chronic renal failure resulting in severe bone disease. Secondary hyperparathyroidism is composed of increased in parathyroid hormone (PTH) synthesis THE PTH GENEand secretion due to an increase in PTH gene expression andThe parathyroid cell is committed to the synthesis of parathyroid cell proliferation. PTH gene expression is regulated by calcium, phosphate and 1,25-dihydroxy vitamin D PTH, implying that there are specific trans-and cis-fac-(1,25(OH) 2 D). 1,25(OH) 2 D 3 injected to rats leads to a dramatic tors acting on the PTH gene that are specific to the cell decrease in PTH gene transcription without any increase in and gene. The gene itself is expressed once in the human serum calcium. Hypocalcemia leads to a large increase in PTH genome and is a relatively simple gene. It has been cloned mRNA levels which is post-transcriptional. Hypophosphatein a number of species and in all species it consists of mia leads to a marked decrease in PTH gene expression that is also post-transcriptional. The mechanisms of the post-tran-three exons and two introns. These exons code for the scriptional effects of calcium and phosphate on the PTH gene 5Ј-untranslated region and the presequence of the gene, have shown to be due to changes in protein-RNA interactions the pro-sequence and for the translated hormone and at the PTH mRNA 3Ј-UTR. Hypocalcemia leads to increased the 3Ј-untranslated region, respectively. The PTH gene binding of parathyroid cytosolic proteins to the PTH mRNA 1 C.Y. was on sabbatical leave from Erciyes University Medical School, cium [3]. There is a subsequent decrease in PTH secretion. Kayseri, Turkey.