The -6.1-kilobase chicken lysozyme enhancer is a multifactorial complex containing several cell-type-specific...

Area of Science:

• * Molecular biology
• * Gene regulation
• * Epigenetics

Background:

• * The chicken lysozyme gene locus is activated in myeloid and oviduct cells.
• * A DNase I-hypersensitive site upstream of the gene suggests regulatory involvement.
• * This region functions as a cell-type-specific transcriptional enhancer in myeloid cells.

Purpose of the Study:

• * To delineate the minimal DNA sequence responsible for promacrophage-specific enhancer activity.
• * To identify the functional elements within the enhancer region.
• * To investigate the role of DNA-binding proteins in mediating cell-type specificity.

Main Methods:

• * Deletion analysis to identify the minimal enhancer fragment.
• * Point mutation analysis in transient gene transfer experiments.
• * In vitro DNA-binding assays to assess protein interactions.

Main Results:

• * A 157-bp minimal fragment retains promacrophage-specific enhancer activity.
• * The minimal enhancer contains at least six functional elements, including NF-I/TGGCA binding sites and AP1/octanucleotide homologies.
• * Mutation of the NF-I binding site abolished both in vitro binding and in vivo enhancer activity.
• * Overlapping oligonucleotides conferred myeloid-cell-specific activity, indicating complex interactions.
• * Several myeloid-cell-specific DNA-binding proteins were identified interacting with the enhancer.

Conclusions:

• * The -6.1 kb enhancer is a compact, multifactorial regulatory complex.
• * Multiple adjacent elements contribute to enhancer function.
• * Cell type specificity is mediated by interactions with more than one trans-acting factor.