sequencing is that DNA modifications can be detected. "Let's say some base has a methyl attached to it. With Sanger's method, you cannot [identify] that because you replicate the DNA using extender bases, so you'd never know," says Chen. "With the Maxam-Gilbert method and mass spectrometry detection, you measure the molecular weight [of fragments of the original template], so you can know whether the DNA base has been modified." If Maxam-Gilbert sequencing has advantages over Sanger sequencing, why
CE tackles protein complexes
has it taken so long for mass spectrometrists to try it? Chen speculates that it's because mass spectrometric DNA sequencing is still in the beginning stages, and because people who don't need to sequence the "difficult" templates are more likely to use Sanger sequencing, which is widely available in kits. Furthermore, the Sanger chain termination method yields cleaner samples for MS sequencing, so longer sequences of DNA can be determined. There's still work to do before this method will compete with gel electrophore-
sis, the workhorse of the DNA-sequencing community. Although the difficult templates may represent only 10% of the genome, that 10% could "create tremendous headaches" for the completion of the human genome, says Chen. "If we can develop this technology, we should be able to help eventually complete the whole sequence. It's difficult for them to use gel electrophoresis for doing [the difficult templates] ," he says. "We need to improve our resolution to apply the method to human genome sequencing." Celia Henry
"With automation, [the CE/MS/MS method] could be quite useful for the identification of proteins involved in lowabundance protein complexes, such as signaling pathways and transcription complexes," says Yates. He points out that an obvious place for the work to be applied is in the field of proteomics—the study of proteins and the analysis of disease and drug effects on gene expression and in the identification of new mo-
tion was achieved by connecting a microelectrospray tip to the CE column using a PEEK tee, similar to that used Researchers at the University of in LC microelectrospray. Design Washington-Seattle have extended changes to the basic configuration CE/MS/MS techniques to the analyeliminated the background ions prosis and identification of complex produced by stainless steel at the electritein mixtures. Although correspondcal connection. The analysis was pering author John Yates says the work is formed in
