Researchers from Harvard Medical School, USA, have discovered a new type of gene with a regulatory function, which might help us to understand why 95% of chromosomes are made up of 'junk' DNA.

In Nature (3 June 2004), Fred Winston and colleagues show that the SRG1 gene in yeast represses its next-door neighbour, SER3, using a transcription-interference mechanism. SRG1 transcription across the SER3 promoter hinders activator binding.

The authors studied the SER3 gene because it is repressed by a common transcriptional activator complex. When they analysed SER3, they were surprised to find that all the factors necessary for transcription were just upstream of the SER3 promoter, despite the fact that the gene was switched off. However, they then noticed a TATA box upstream of SER3, which could signify the promoter of a new gene. They showed that this gene — SRG1 — is highly transcribed, but that is does not encode a protein. It is the active transcription of SRG1 that represses SER3 transcription.

Winston said, “This doesn't explain all junk DNA. It gives a potential use for some junk DNA.” “We found one example of a type of regulatory gene that hasn't been found before that might alert investigators to look for it in other cases” (Reuters AlertNet, 2 June 2004).

“Our guess is that more examples will be found, and this will be really illuminating”, Winston added (The Scientist, 3 June 2004). So, the challenge now is to find other examples of this type of regulation and to understand how this type of gene regulation is controlled.