Small RNAs for defence and regulation in archaea

Abstract

Non-coding RNAs are key players in many cellular processes within organisms from all three domains of life. The range and diversity of small RNA functions beyond their involvement in translation and RNA processing was first recognized for eukaryotes and bacteria. Since then, small RNAs were also found to be abundant in archaea. Their functions include the regulation of gene expression and the establishment of immunity against invading mobile genetic elements. This review summarizes our current knowledge about small RNAs used for regulation and defence in archaea.

Fig. 1

Schematic overview of the CRISPR/Cas type I mechanism. A viral sequence (protospacer, red) is incorporated into the host CRISPR cluster (R indicates repeat sequences). The universal Cas1 and Cas2 proteins are proposed to mediate this adaptation step. The CRISPR cluster is transcribed into a pre-crRNA that is processed into mature crRNAs by Cas6. The crRNAs are loaded onto the Cascade complex that delivers crRNA to the viral DNA during a repeat attack. The virus is identified via base complementarity between crRNA and protospacer and is subsequently degraded by Cas3 (color figure online)

Fig. 2

Correlation of archaeal and bacterial growth temperatures with CRISPR/Cas content. Over 50 archaeal (a, b) and bacterial (c, d) genomes were analyzed for number of CRISPR and cas genes, respectively, and compared to the respective optimal growth temperatures. Indicated is the best-fit line of raw data. Significance of correlation was confirmed by Spearman’s rank correlation test (a ρ = 0.459, b ρ = 0.602, c ρ = 0.609, d ρ = 0.602; a–d p < 0.001)