d proteins, Max and Mnt) binds to in the fly genome. The researchers employed a so-called "DamID approach" to tag Myc-binding sites. By expressing a fusion protein of the bacterial Dam methylase enzyme with Myc in fly cells, Dr. Eisenman and colleagues were able to mark each region of Myc binding with methyl groups. The presence of these "methylation markers" enabled the researchers to distinguish regions of direct Myc-binding from the rest of the genome, isolate the sequences of interest, and then use microarray analysis to identify the encoded genes.

In contrast, Dr. Amati's group used human cells to identify Myc target genes. The researchers focused on those genes that bind Myc through the consensus "E-box" DNA sequence (CACGTG). Dr. Amati and colleagues used bioinformatics tools to scan the human genome and identify genes containing one or more E-boxes in the proximity of their promoter (the portion of the gene where transcription begins). Of the 1630 gene loci identified, approximately 700 underwent further biochemical characterization to determine which E-box-containing genes bind Myc in vivo. As in flies, the results were surprising.

As Dr. Amati explains, "In addition to identifying 257 genes that are bound by Myc in the human genome, our data also reveals that Myc must bind at least one tenth of all cellular genes or, in other words, several thousand genes. This unexpected degree of complexity is a fundamental feature that is conserved between humans and flies."

Taken together, these two studies provide the most comprehensive enumeration of direct, in vivo Myc targets. The conclusion that Myc binds a large portion of both the fly and human genome dramatically alters previous views of Myc's activity and the complexity of its biological interactions. Rather than consider a limited number of genes to be targets of Myc, it is now apparent that Myc exerts an extremely widespread influence over the vertebrate genome.

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Contact: Heather Cosel
coselpie@cshl.org
Cold Spring Harbor Laboratory
29-Apr-2003

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