Albany 2015:Book of Abstracts
June 9-13 2015
©Adenine Press (2012)
Pseudo-Lamarckian Spacer Adaptation by Type I CRISPR-Cas System
CRISPR-Cas systems are common in prokaryotes and can provide small RNA-based adaptive immunity against mobile genetic elements. A CRISPR-Cas system consists of DNA loci with Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR associated (cas) genes. The CRISPR locus is composed of an array of identical or very similar repeats separated by spacers of common length but variable sequence. Small CRISPR RNAs containing a single spacer sequence, in complex with Cas proteins, detect DNA molecules complementary to CRISPR RNA spacer element and target them for destruction. Some spacers originate from viruses parasitizing on a prokaryotic host and the presence of such spacers can make the cell resistant to genetic parasites with sequences matching CRISPR spacers of the host. The process of acquisition of new CRISPR spacers in the course of infection of naïve host is obviously adaptive and appears to be Lamarckian in nature. We will present evidence that despite this appearance, adaptive CRISPR spacer acquisition is underlined by a purely Darwinian, random acquisition of spacers from both bacterial host and infecting viral DNA, followed by counter selection against bacteria that acquired host-derived spacers through an auto-immune CRISPR-Cas system function and positive selection of clones that acquired virus-derived spacers.
Datsenko, K. A., Pougach, K., Tikhonov, A., Wanner, B. L., Severinov, K. & Semenova, E. (2012). Prior encounters dramatically stimulate adaptive bacterial CRISPR immune response to viruses. Nature Commun., 3, 945.
Konstantin Severinov1, 2
1Waksman Institute for Microbiology