Abundance and recognition of tRNA CCACCA extensions as well as 3′-trailer sequences in E. coli. (A) Boxplots of the fraction of E. coli CA244 wt and Δcca tRNAs during exponential (log) and stationary (stat) growth carrying CCACCA extensions. Values are given as a fraction of respective tRNA subpopulations normalized to the total tRNA reads for each isoacceptor. (B) Nucleotide frequencies within the 3′-trailer region of the E. coli K12 tRNA genes starting from the CCA triplet (weblogo.berkeley.edu). Letter height correlates with abundance; A and U residues are highlighted in gray. (C) Radiolabeled E. coli tRNAAla with either its native 3′-trailer (CCAAAU, left) or the corresponding degradation tag (CCACCA, right) was incubated with either RNase R (upper panel, 20 ng µL−1) or RNase T (lower panel, 0.6 ng µL−1). Assays were carried out in a 40 µL total reaction volume with 5 µM tRNA substrate. C, control reactions without enzyme incubated for the maximal reaction time; M, size marker tRNAAla, 73 nt.