Frances Crick said it first. Five years after he and James Watsondescribed DNA's double helix in 1953, Crick enunciated the "centraldogma" of molecular biology. It makes the assumption that geneticinformation can be passed on from DNA to RNA, and from RNA toprotein, but cannot flow backward from protein to RNA to DNA.

A few years ago, this basic truism came into the mind of moleculargeneticist and cell biologist Jonathan Jarvik, of Carnegie MellonUniversity in Pittsburgh. He was wrestling with the proteincomposition of a single-cell green alga, Chalmidomonas rheinhardii(not to be confused with the Chlamidia pathogen).

C. rheinhardii is bigger than a bacterium, but smaller than a typicalmammalian cell. It's a prime ingredient of the green scum onfreshwater ponds and ditches, and thought to be an evolutionaryancestor of all plant life on earth. The alga navigates arround itswatery habitat propelled by a pair of whiplike flagella.

"We were interested in understanding the flagella transition region,"Jarvik told BioWorld Today, "where the basal body within the cellmeets the flagellum extending out. It's really a projection of themembrane that goes all the way around the cell, like a finger in aglove.

"We wanted to identify the proteins in that region where those twojoin," he continued, "as well as the genes that encode those proteins.So the issue before us was how were we going to identify individualproteins against a background of nearly all the other proteins in thecell."

At that point, Crick's "central dogma" prompted Jarvik to invent theapproach or technology that he calls "CD-tagging" _ CD for centraldogma.

His research report describing the invention appears in the May issueof BioTechniques, titled "CD-Tagging: A new approach to gene andprotein discovery and analysis."

This consists essentially of inserting a short stretch of DNA, the CDcasette, into an intron _ a non-translating sequence _ of a targetgene. This open reading frame is flanked by splice acceptor anddonor sites. When the intron is splice-excised during assembly of thegene's exons prior to translation, that synthetic nucleotide sequencebecomes a new "guest exon," carried along into the messenger RNAand subsequently expressed as a specific peptide sequence in the finalprotein.

"Because these tags are unique," Jarvik explained, "specificnucleotide or antibody probes can be used to obtain and/or analyzethe gene, RNA transcript or protein."

Jarvik's paper describes how he applied this through-put approach tothe molecular structures of C. rheinhardii's flagella, as well as to agene of the fruit fly, Drosophila melanogaster. He has since made itwork to epitope-tag mammalian genes _specifically those of mice_ using a retroviral delivery vector.

"CD-tagging's greatest utility," he suggested "will be in the realm ofgene discovery. Unlike methods in current use, it can be used todiscover genes at the true level of function for most genes _ theprotein level."

Asked how this method might be applied to therapy and diagnosticsof human disease, Jarvik answered the question with a question:"What's the value of gene discovery and protein discoverydevelopment for therapeutics?" His reply: "In what until recently wascalled the biotech industry _ now people like to call itbiopharmaceuticals _ most products that have made it to themarketplace are proteins. For example, growth factors, cytokines,hormones."

He went on: "Then when you get into classical pharmaceuticals,where the drug is typically a small molecule, what's the target?Almost always _ 99 percent _ a protein."

Starting July 1, 1996, Jarvik will begin a 12 to 15 month sabbaticalfrom his faculty position at Carnegie Mellon, as vice president forbiology at Vyrex Corp. in San Diego. That company's generalcounsel, Carl Lewis, explained to BioWorld Today:

"The CD-tagging technology was developed by Dr. Jarvik outside hiswork at the university, which did not fund it. So, based on CarnegieMellon's policy, it's his proprietary technology, and the pendingpatent is in his name."

Lewis continued: "He has made over his rights to the company, inconsideration of being named a vice president, with a stock option ofpretty substantial size."

Biochemist and molecular biologist Sheldon Hendler is president andchairman of Vyrex. "We're already developing the CD-taggingtechnology at several levels, he told BioWorld Today, "beginningwith epitope-tagging kits for molecular and biochemical researchpurposes in house. That's being done with American Qualex Inc., ofSan Clemente, Calif.

"Then, we're actively pursuing the retroviral vector with mouse cells,while really waiting for Dr. Jarvik to come to us in July, so we canstrategize as to what we're going to do. One thing we're thinking of isusing this technology in looking at prostate cancer, although wehaven't yet worked out the details." n

-- David N. Leff Science Editor

(c) 1997 American Health Consultants. All rights reserved.