Scientists say they've determined the process by which bacteria "steal" some genetic information in viruses, and similar invading bodies, and make use of it to create immunological "memory."
The discovery could lead to improvements in genetic editing in an effort to treat illness and genetic diseases, researchers at the Lawrence Berkeley National Laboratory in California say.
"We've shown that bacteria need only two proteins to facilitate this process, Cas1 and Cas2," says Jennifer Doudna, a biochemist in the Physical Biosciences Division of the Bekeley lab. "Our findings could provide an alternative way of introducing needed genetic information into a human cell or correcting a problem in an existing genome."
Bacteria experience a continuous assault by viruses and plasmids, pieces of nucleic acid, and to survive they deploy a number of defenses, including an adaptable immune system built around a type of of DNA called CRISPR.
Standing for Clustered Regularly Interspaced Short Palindromic Repeats, a unit of CRISPR DNA consists of "repeating" elements of nucleotides separated by unique "spacer" elements of variable sequences of nucleotides.
Using the "Cas" proteins identified by the researchers, bacteria are capable of silencing critical sections of the genetic information of a foreign invader and by "remembering" the infection, generate immunity from related future invasions.
"We've learned that bacteria can acquire critical pieces of genetic information from foreign invaders and insert this information into the CRISPR loci within their own genome as new spacers," says study lead author James Nuñez.
The spacers derived from the foreign invader serve as a sort of memory bank, he explains.
Working with E. coli bacteria, the researchers discovered the Cas memorizing proteins could recognize repeating element sequences within CRISPR locations and target those sites as locations for insertion of spacers.
The proteins determine "precisely where to place the spacer sequences from a foreign invader, a virus or a plasmid," Nuñez explains. "When the process is completed, the host bacterium is now immune to future infections from that same type of virus or plasmid."
In the future it could be possible to program the proteins for a desired DNA sequence and introduce them into human cells as a treatment for disease or genetic abnormalities, the researchers say.
"It turns out that bacteria ... have been using Cas1 and Cas2 proteins in their immunization process for millions of years," says Nuñez.
The researchers' next task is to understand the rules that guide that process and learn how to apply them in human cells, he says.
