Lewis A. Chodosh

Bio: Lewis A. Chodosh is an academic researcher from Harvard University. The author has contributed to research in topics: Protein subunit & Binding site. The author has an hindex of 2, co-authored 2 publications receiving 1204 citations. Previous affiliations of Lewis A. Chodosh include Massachusetts Institute of Technology.

A genomic sequencing protocol that yields a positive display of 5-methylcytosine residues in individual DNA strands.

Abstract: The modulation of DNA-protein interactions by methylation of protein-binding sites in DNA and the occurrence in genomic imprinting, X chromosome inactivation, and fragile X syndrome of different methylation patterns in DNA of different chromosomal origin have underlined the need to establish methylation patterns in individual strands of particular genomic sequences. We report a genomic sequencing method that provides positive identification of 5-methylcytosine residues and yields strand-specific sequences of individual molecules in genomic DNA. The method utilizes bisulfite-induced modification of genomic DNA, under conditions whereby cytosine is converted to uracil, but 5-methylcytosine remains nonreactive. The sequence under investigation is then amplified by PCR with two sets of strand-specific primers to yield a pair of fragments, one from each strand, in which all uracil and thymine residues have been amplified as thymine and only 5-methylcytosine residues have been amplified as cytosine. The PCR products can be sequenced directly to provide a strand-specific average sequence for the population of molecules or can be cloned and sequenced to provide methylation maps of single DNA molecules. We tested the method by defining the methylation status within single DNA strands of two closely spaced CpG dinucleotides in the promoter of the human kininogen gene. During the analysis, we encountered in sperm DNA an unusual methylation pattern, which suggests that the high methylation level of single-copy sequences in sperm may be locally modulated by binding of protein factors in germ-line cells.

How eukaryotic transcriptional activators work

Abstract: A specific protein, bound to DNA, can activate transcription of a wide array of genes in many eukaryotes. Further analysis suggests a general outline for how eukaryotic transcriptional activators function and are controlled.

Max: a helix-loop-helix zipper protein that forms a sequence-specific dna-binding complex with myc and mad

Abstract: Nucleic acid molecules capable of hybridizing under stringent conditions to the nucleotide sequence residing between positions 1 and 453 of the max cDNAs shown in Figure 2, or to the nucleotide sequence reisiding between positions 148 and 810 of the mad cDNAs shown in Figure 14. The Max polypeptide when associated with the Myc or Mad polypeptide is capable of binding to nucleotide sequences containing CACGTG.

The Cell Cycle

Abstract: 5 The activity of cyclin-dependent protein kinase p34cdc2 is regulated by phosphorylation. In this study, we show that the presence of phosphatase inhibitors can have major effects on the levels of phosphorylation and the activities of the kinase extracted from cells. The combination of okadaic acid and sodium vanadate was most effective in protecting p34cdc2 against cellular phosphatases. In the absence of these inhibitors, p34cdc2 was dephosphorylated with an altered activity, indicating that phosphatase activities remained high during extractions. In contrast to when both inhibitors were used, lower activity of the kinase was found when only sodium vanadate was used, whereas higher activity was found in the presence of okadaic acid. Other conventional phosphatase inhibitors such as NaP, NaRS03 and glycero12-phosphate, were not effective in preventing dephosphorylation from p34cdc2 in whole cell lysates.