Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: RNA pseudoknots are structural elements that participate in a variety of biological processes. At À1 ribosomal frameshifting sites, several types of pseudoknot have been identi®ed which differ in their organisation and functionality. The pseudoknot found in infectious bronchitis virus (IBV) is typical of those that possess a long stem 1 of 11-12 bp and a long loop 2 (30-164 nt). A second group of pseudoknots are distinguishable that contain stems of only 5 to 7 bp and shorter loops. The NMR structure of one such pseudoknot, that of mouse mammary tumor virus (MMTV), has revealed that it is kinked at the stem 1-stem 2 junction, and that this kinked conformation is essential for ef®cient frameshifting. We recently investigated the effect on frameshifting of modulating stem 1 length and stability in IBV-based pseudoknots, and found that a stem 1 with at least 11 bp was needed for ef®cient frameshifting. Here, we describe the sequence manipulations that are necessary to bypass the requirement for an 11 bp stem 1 and to convert a short non-functional IBV-derived pseudoknot into a highly ef®cient, kinked frameshifter pseudoknot. Simple insertion of an adenine residue at the stem 1-stem 2 junction (an essential feature of a kinked pseudoknot) was not suf®cient to create a functional pseudoknot. An additional change was needed: ef®cient frameshifting was recovered only when the last nucleotide of loop 2 was changed from a G to an A. The requirement for an A at the end of loop 2 is consistent with a loop-helix contact similar to those described in other RNA tertiary structures. A mutational analysis of both partners of the proposed interaction, the loop 2 terminal adenine residue and two G ÁC pairs near the top of stem 1, revealed that the interaction was essential for ef®cient frameshifting. The speci®c requirement for a 3 H -terminal A residue was lost when loop 2 was increased from 8 to 14 nt, suggesting that the loop-helix contact may be required only in those pseudoknots with a short loop 2.

Evidence for an RNA Pseudoknot Loop-Helix Interaction Essential for Efficient À1 Ribosomal Frameshifting