Table 1 Sequence features associated with strand selection in human and fly miRNAs

All annotated miRNA and new microRNA*

First nuclotide

U (36%)

U (51%)

Purine or Pyrimidine bias

No

No

Strand-biased miRNA

Selected strand

First nucleotide

U (79%)

U (80%)

Purine bias

Yes

No

Excluded strand

First nucleotide

C (76%)

C (37%) G (27%)

Pyrimidine bias

Yes

No

GC basepair

25/33 (76%)

15/30 (50%)