Multiple levels of gene control in eukaryotic cells

A role for the nucleotype in the pathogenesis of primary hepatocellular carcinoma

The risk of developing primary hepatocellular carcinoma (HCC) is 200 times higher for chronic carriers of hepatitis B virus antigen (HBsAg) than for the rest of the population. There is experimental evidence which suggests that the expression of viral DNA sequences integrated into the host's genome directly contributes to HCC development. However, most evidence available suggests that development of HCC requires a second genetic event that results from the chronic hepatitis and cirrhosis observed in symptomatic HBsAg chronic carriers. Here it is argued that the nucleotype, defined as those non-genic characters of nuclear DNA that affect or control the phenotype, is the element that links the viral, cellular and host factors involved in the genesis of HCC.

On the regulation of DNA methylation by higher-order structure in the cell nucleus

Several years ago it was postulated that DNA methylation may play a role in the regulation of gene activity in animal cells. Progress has been made in establishing the mechanisms by which methylation influences gene expression, but little is known about the mechanisms that control methylation itself. Here is proposed a model, susceptible of experimental confirmation, which suggests that chromatin higher-order structure is a determinant factor for the regulation of DNA methylation. The background for such a model as well as current evidence in support of it are discussed.

Nucleotide sequence of a gene from chromosome 1D of wheat encoding a HMW-glutenin subunit

A high molecular weight glutenin gene in hexaploid wheat has been isolated by cloning in bacteriophage lambda and characterized. The gene corresponds to polypeptide 12 encoded by chromosome 1D in the variety "Chinese Spring". The coding sequence predicted contains seven cysteine residues six of which flank a central repetitive region comprising more than 70% of the polypeptide. These findings are related to the role of high molecular weight subunits in the viscoelastic theory of gluten structure.