Programmed mRNA cleavage by L. lactis type III-A crRNPs expressed in E. coli. (A) Diagram of a representative type III-A effector crRNP containing Csm1-5 subunits and a crRNA, in the process of cleaving a bound target RNA. Each Csm3 RNase subunit cuts the target RNA once (cleavages indicated by arrows) within the region of the target RNA (orange) that base-pairs with the crRNA guide element (blue). The position of the target RNA protospacer flanking sequence (PFS) is indicated as are the HD (DNase) and Palm (cyclic oligoadenylate [cOA] producing) motifs of the Csm1 subunit. (B–D) Expression of L. lactis type III-A crRNPs containing either a crRNA against the lpp mRNA (lpp) or negative control crRNA (C) was induced (+), and northern analysis was performed using probes against the lpp mRNA (B), lpp crRNA (C), control crRNA (D), or constitutively expressed 5S rRNA (C,D). The positions of the RNAs are indicated, including those of the full-length lpp mRNA (dot) and lpp mRNA cleavage products (red star). The dotted line in B indicates that intervening lanes were omitted from the blot. The sizes of the molecular weight markers (M) are indicated in each panel.
