In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In parallel , total RNA was extracted from samples of dissected heart and analyzed by Northern blot hybridization to determine the steady - state level of three RNA transcripts encoded by the COXII , COXIII , and COXIV genes .
### Output Text:
In parallel , total RNA was extracted from samples of dissected heart and analyzed by Northern blot hybridization to determine the steady - state level of three RNA transcripts encoded by the COXII , COXIII , and COXIV genes . 