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Falcon synthesizes the primary and review literature to assign zebrafish pcif1/CAPAM
as the cap-specific m6Am writer that methylates the cap-adjacent adenosine of capped mRNAs.
"CAPAM/PCIF1 is the **cap-specific** methyltransferase that writes this **m6Am** mark at the transcription start nucleotide."
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Falcon notes CAPAM is a SAM-dependent N6-adenosine methyltransferase using SAM as
methyl donor, consistent with the GO:1904047 SAM-binding annotation.
"CAPAM/PCIF1 is a **SAM-dependent N6-adenosine methyltransferase** that installs **m6Am** at the cap-adjacent nucleotide of mRNAs."
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Falcon reports PCIF1 is predominantly nuclear, supporting the nucleus localization annotations.
"PCIF1 is described as primarily **nuclear**"
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Falcon reports the WW domain binds Ser5-phosphorylated RNA polymerase II CTD, enabling
co-transcriptional deposition; this supports GO:0099122 as a recruitment/association feature
rather than the core catalytic activity.
"its WW domain binds the **Ser5-phosphorylated C-terminal domain (CTD)** of **RNA polymerase II**, consistent with recruitment to early transcription complexes and **co-transcriptional** installation of m6Am at transcription start sites."
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Falcon identifies direct zebrafish-specific evidence: m6Am is detectable in zebrafish mRNA
and zebrafish CAPAM (zCAPAM) was used in crystallographic structure determination.
"m6Am is detectable in zebrafish mRNA"
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Falcon notes CAPAM acts specifically at the 5' cap-adjacent position and does not methylate
internal Am, distinguishing this writer activity from internal m6A methyltransferases.
"CAPAM does **not methylate internal Am**"