Separate aminoacyl transfer centers related to the small …GUNNN..: NNNU ribozyme seem possible at the frequent GU sequences dispersed throughout an RNA tertiary structure. In fact, such activity is easily detected and varies more than 2 orders in rate, probabably being faster at sites with less structural constraint. Analysis of a particular constrained active site in an rRNA transcript suggests that its difficulty lies not in substrate strand association, but in binding and/or group transfer from the aminoacyl precursor. Efficient aminoacyl transfer requires accurate complementarity between large or small ribozymes and oligoribonucleotide substrates, even when only three or four base pairs link the two. Thus, multi-site active ribozymal superstructures might have coordinated an RNA metabolism, including aiding an early translation apparatus.