1
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Before mRNA can be used by ribosomes as a template for building proteins, it must first be processed.

2
00:00:26,339 --> 00:00:31,339
Key steps are the addition of a methylated cap and a polyadenylated tail.

3
00:00:31,339 --> 00:00:39,340
Involved in processing are RNA polymerase, cleavage factors, and poly A polymerase.

4
00:00:39,340 --> 00:00:44,710
Processing of mRNA begins with transcription.

5
00:00:44,710 --> 00:00:53,119
Soon after RNA polymerase begins transcription, a methylated cap is added to the 5' end.

6
00:00:56,530 --> 00:00:58,670
Transcription then continues to completion.

7
00:01:00,590 --> 00:01:05,430
Following completion, RNA polymerase releases the capped strand of pre-mRNA.

8
00:01:08,790 --> 00:01:13,349
Specific nucleotide sequences in the mRNA are bound by cleavage factors.

9
00:01:16,599 --> 00:01:21,620
The 3' end of the mRNA is next moved into the correct configuration for cleavage.

10
00:01:23,959 --> 00:01:26,780
Stabilizing factors are then added to the complex.

11
00:01:28,439 --> 00:01:33,340
Poly-A polymerase now binds to the mRNA and cleaves the 3' end.

12
00:01:34,079 --> 00:01:38,620
The complex begins to dissociate and the cleaved 3' end quickly degrades.

13
00:01:39,780 --> 00:01:47,519
Poly-A polymerase now synthesizes the polyadenylated tail by adding adenine residues to the cleavage site.

14
00:01:48,159 --> 00:01:52,700
Additional proteins then bind to the tail, increasing the rate at which it grows.

15
00:01:53,060 --> 00:01:57,840
When the tail reaches its full length, the poly-A polymerase is signaled to stop adding

16
00:01:57,840 --> 00:02:01,400
residues, and the polyadenylation process is completed.

17
00:02:02,739 --> 00:02:08,439
The processed mRNA is now ready to undergo splicing in preparation for translation.