# Dada2 trimming question

**URL:** https://forum.qiime2.org/t/dada2-trimming-question/907
**Category:** User Support
**Tags:** dada2
**Created:** [July 28, 2017, 8:55pm UTC](https://forum.qiime2.org/t/dada2-trimming-question/907 "2017-07-28T20:55:34Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![benjjneb](https://forum.qiime2.org/user_avatar/forum.qiime2.org/benjjneb/32/1602_2.png) [@benjjneb](https://forum.qiime2.org/u/benjjneb)
#### Post date: [July 31, 2017, 8:06pm UTC](https://forum.qiime2.org/t/dada2-trimming-question/907/2 "2017-07-31T20:06:37Z")

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If you compare the start of your sequences to the Illumina adapter/primer sequences, you will see they match in the second-half:

```
                                 CCTACGGG
TCGTCGGCAGCGTCAGATGTGTATAAGAGACAGCCTACGGGNGGCWGCAG

                                  NACTAC
GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAGGACTACHVGGGTATCTAATCC

```

Those are the 341F and 805R primers, and they need to be removed. You can do so here with `trim-left-f 17` and `trim-left-r 21`, which you can read off the above.

This amplicon is longer than the reads, so they won't read into the other primer, hence `trunc-len` is not needed for primer removal.

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