Structure and tissue-specific expression of the @entity1 XXXX gene.

@entity1 @entity462 @entity535 @entity15928 @entity20671 @entity157 @entity703
The @entity1 metallothionein ( @entity20671 ) IB gene ( @entity15928 ) is located in a region of @entity1 DNA containing at least four tandemly arranged @entity20671 genes. As deduced from its sequence, @entity15928 is likely to encode a functional protein. However, the predicted @entity535 sequence differed from the @entity20671 -I @entity535 sequence in four positions. Most remarkable was the presence of an additional @entity462 . Like other @entity20671 genes, @entity15928 has at least two copies of the metal-responsive element upstream from the transcription initiation site. These elements probably are responsible for the metal responsiveness of the @entity15928 promoter, leading to inducible expression of fused heterologous genes. Unlike the @entity20671 -IIA and @entity20671 -IA genes described previously, which are expressed in many different cell types, a high level of expression of the endogenous @entity15928 gene could be detected only in @entity1 @entity157 and @entity703 cell lines. Therefore, this is the first @entity20671 gene described which exhibits tissue specificity of expression. This specificity is controlled by a cis-acting mechanism involving methylation, since incubation of nonexpressing cells with an inhibitor of DNA methylation led to activation of the @entity15928 gene. In support of this notion, we found that the 5' flanking region of the @entity15928 gene was highly methylated in HeLa cells, a nonexpressing cell type, but it was not methylated in a @entity157 (expressing) cell line.
