Table 1. Composite and transposed C/D box sRNAs.

C/D box sRNA	Type	D′ guide	D guide
Pca sR12/45	Composite	Shared with sR45 family D′ guide	Shared with sR12 family D guide
Pca sR103/109	Composite	Shared with sR103 family D′ guide	Shared with sR109 family D guide
Pca sR26a	Transposed	Shared with sR26 family D guide	Not shared
Pae sR57a	Transposed	Not shared	Shared with sR57 family D guide
Pca sR57b	Transposed	Shared with sR57 family D guide	Not shared
Par and Pog sR13a	Transposed	Shared with sR13 family D guide	Not shared

Two unusual types of sRNAs (composite and transposed) were identified. Composite sRNAs have a D guide that shows sequence similarity to a guide in one sRNA family, whereas the D′ guide shows sequence similarity to a guide from a second sRNA family. These are given both family numbers separated by a forward slash (/). Transposed sRNAs have either a D guide that is shared with the D′ guide of the defining family, or vice versa, a D′ guide that is shared with the D guide of another family. Transposed sRNAs are identified with the number of the defining family followed by a lower-case a or b. The Pae sR57a is considered as a transposed sRNA since the D′ guide normally associated with the sR57 is not present (to view these sRNA sequences, see http://lowelab.ucsc.edu/snoRNAdb/).