Table 3.

Distributions of all 25-nt segments of the MAC genome beginning with 5′-TNG, and of 5′-UNG, 25-nt MAC scnRNAs, over annotated features of the MAC genome

Features	5′TNG in MAC genome		5′UNG MAC scnRNAs		Statistical test
	Numbers	Frequencies	Observed	Expected (e)	χ2	P-value
Intergenic regionsa	1265012	0.169	31	29.3	0.06	0.80
Coding exons,b sense str.	2922337	0.391	71	67.6	0.21	0.65
Introns,c sense str.	246029	0.033	5	5.7	0.01	0.94
Coding exons,b antisense str.	2859122	0.382	61	66.1	0.52	0.47
Introns,c antisense str.	181929	0.024	4	4.2	0.02	0.89
Otherd	6469	0.001	1	0.1	0.82	0.36
Total	7480898	1.000	173	173.0

^aMany scnRNAs mapping to intergenic regions may be part of non-coding exons, because intergenic regions are very short (352 bp on average) and most 5′ and 3′UTRs have not been annotated.

^bscnRNAs mapping in coding exons, including those overlapping 5′ or 3′UTRs, but excluding those overlapping introns.

^cscnRNAs overlapping intronic sequences. Because introns are very short (25 nt on average), very few scnRNAs are expected to be entirely within introns.

^dAll other cases. The one case observed overlaps the coding sequences of two closely spaced, convergent genes.

^eRandom expectation is based on the actual distribution of 25 nt, 5′-TNG segments of the MAC genome. The non-significant P-values in the last column (Pearson's χ² test with Yates’ continuity correction) indicate that the fractions of scnRNAs mapping to the different types of annotated features are consistent with a random distribution (confirmed by a χ² test comparing observed and expected distributions, P = 0.35).