Fig. 4.

Influence of 5’-guanosine number on RNA function. (A) Disruption of a single base pair (C57-G103) by C57 to G mutagenesis disrupts ^Cap1G-L³⁷¹ dimerization. Compensatory G103C substitution substantially restores dimerization. (B) eIF4E binds ^Cap3G-L³⁷¹ (C denotes the eIF4E:RNA complex) but not the non-capped RNA. (C) At low ionic strength, eIF4E binds the M conformer of ^Cap1G-L³⁵⁹, butnotM* or the ^Cap1G-L^Lock construct. (D) Similar results were obtained in PI buffer. (E-F) The 5’-RNA exonuclease (XRN-1) and decapping enzyme (hDcp2) are independently unable to degrade ^Cap1G- or ^Cap3G-leader RNAs. In the presence of both enzymes, The ^Cap1G-L^Lock resists degradation over time (E) and with increasing hDcp2 (F) compared to the cap-exposed ^Cap3G-L³⁷¹ leader. (G) Mechanism for transcriptional control of HIV-1 RNA function. Capped RNAs containing two or three 5’-guanosines adopt a monomeric structure that exposes the cap and enables RNA processing and metabolism, whereas those with a single capped G adopt a cap-sequestered conformation that promotes dimerization and packaging.