Catalysis of the reaction: UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-L-lysyl-D-alanyl-D-alanine + L-alanyl-tRNA(Ala) = UDP-N-acetylmuramoyl-L-alanyl-D-glutamyl-N6-(L-alanyl)-L-lysyl-D-alanyl-D-alanine + tRNA(Ala).
UDP-N-acetylmuramoylpentapeptide lysine N6-alanyltransferase activity