Reaction catalyzed by (E3-independent) E2 ubiquitin-conjugating enzyme (2.3.2.24)

	[E1 ubiquitin-activating enzyme]-S-ubiquitinyl-L-cysteine	+		[acceptor protein]-L-lysine	=		[E1 ubiquitin-activating enzyme]-L-cysteine	+		[acceptor protein]-N6-monoubiquitinyl-L-lysine
	[E1 ubiquitin-activating enzyme]-S-ubiquitinyl-L-cysteine	+		[acceptor protein]-L-lysine	=		[E1 ubiquitin-activating enzyme]-L-cysteine	+		[acceptor protein]-N6-monoubiquitinyl-L-lysine