Great progress has been made toward the understanding of the molecular and cellular biology of the small intestine. The obtaining of complementary DNA and genomic clones for critical small intestinal proteins has provided the foundation for a detailed analysis of intestine-specific gene expression and differentiation. New insights have been provided into the regulation of intestine-specific gene expression along the horizontal axis from duodenum to ileum and along the vertical axis from crypt to villus. The expression of some intestinal proteins occurs at the level of posttranscriptional regulation. Other proteins are regulated at the level of gene transcription and the interaction between transcription factors and theircis-acting elements in the intestine-specific genes is beginning to be elucidated.
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