Jane M. Magill

PCR amplification following restriction to detect site-specific DNA methylation

A procedure to test for DNA methylation at sites recognized by methylation-sensitive restriction endonucleases is described. The procedure is based on the assumption that the polymerase chain reaction (PCR) will amplify sequences between two primers only if the target DNA is intact after digestion. A carrot (Daucus carota) cell line that is heterozygous for two sequenced alleles ofDc8, a gene which is expressed during the later stages of embryogenesis provided an ideal source of DNA for developing and testing protocols. The promoters of the two alleles differs significantly in length between two sites used for primers, and only one promoter has a GATC (Sau 3A1 orMbo I) site. This allowed development of a protocol where only the sequence lacking the GATC site was amplified to detectable levels following digestion of DNA withMbo I which is insensitive to symmetric methylation withm4C orm5C.

Role of purine base excretion in regulation of purine pools

SummaryWild type and mutant strains of Neurospora crassa excrete hypoxanthine, xanthine, and uric acid, but not adenine or inosine, when exogenous adenine is added to growing cultures. No detectable excretion occurs in the absence of adenine. The de novo pathway of purine biosynthesis was found to influence the excretion, in that a metabolic block immediately prior to IMP significantly decreased the excretion, while a metabolic block immediately after IMP significantly increased the excretion over that of wild type. The purine catabolic pathway, which is sensitive to ammonia regulation, was found to be a key determinant in the amount and type of excretion. Recently, it was suggested that hypoxanthine accumulation is the result of a mechanism to regulate the adenylate pool size (Leung and Schramm, 1978). In this report, the possibility that hypoxanthine excretion controls adenylate and guanylate pool sizes is discussed and the role of the purine nucleotide cycle in hypoxanthine excretion is examined.