Table 1. Variants of base pairing in the common nef β3/β4 RNA fold.

Base position	Base-pair content	Occurrence	% base pairing	Comments
494–500	AU	21	20.2	Only in the 5-base loop
493–501	UA	101
	UG	3	100
492–502	CG	93
	UG	5
	UA	1	95.2
491–503	GU	97	93.3
490–504	UA	90
	UG	11
	GC	1	98.1
489–505	GC	104	100
488–506	GC	104	100
487–507	UA	102
	UG	1	99