About snRNAs and snoRNAs

Some quick survey about snRNAs and snoRNAs:

- snRNA

small nuclear RNAs, ~150nt,  also called uRNA (due to rich of uridylic residues), functions in RNA splicing

There are 1916 snRNAs in the human genome. Their length distribution as below:

 20  1
 40 * 20
 60 ********** 209
 80 ****** 129
100 ************************************************************ 1217
120 ***** 95
140 **** 83
160 ****** 116
180 ** 42
200  3
220  1

- snoRNAs

small nucleolar RNAs, functions in guiding the modification of other ncRNAs, e,g. mainly rRNAs, snRNAs, tRNA. 

snoRNAs form cluster and 

In human genome (GENCODE v19), there are 1457 snoRNA genes. Length distribution as below:

 40 * 9
 60 *********************************** 252
 80 *************************************** 275
100 ************************************************************ 426
120 ************************************************ 342
140 ******** 59
160 ** 11
180 *** 18
200 ******** 56
220  3
240  1
260 * 4
280  0
300  0
320  1

Some of them have many copies and cluster in a imprinting gene locus (http://www.geneimprint.com/site/genes-by-species), e.g.  SNORD113 and SNORD114 are clustered and located in intron of MEG8, a long ncRNA only maternally expressed. 

And the number of snoRNA copies in the cluster is associated with diseases. e.g. Loss of the 29 copies of SNORD116 (HBII-85) from this region has been identified as a cause of Prader-Willi syndrome whereas gain of additional copies of SNORD115 has been linked to autism.