Maturase K (MatK) is the chloroplast-encoded intron maturase of field pennycress, typically encoded within the intron of the plastid trnK-UUU (lysine tRNA) gene. It is the only maturase retained in the plastid genome and acts as a trans-acting splicing factor that binds intron RNA and promotes excision of a conserved set of chloroplast group IIA introns (including its own trnK host intron and introns in trnA, trnI, trnV, atpF, rpl2 and rps12). It functions in the chloroplast stroma. MatK retains the maturase "domain X" and a degenerate reverse-transcriptase-like region but lacks the endonuclease/mobility domains of canonical bacterial intron-encoded proteins. The gene is also widely used as a plastid DNA barcode and phylogenetic marker.
The preferred accession for this review is Q9GF35. These relationships are manually assessed.
REFERENCE PROTEOME EQUIVALENT · Reviewed 2026-10-19
Reference proteome: UP000836841
Retain Q9GF35 as the primary Swiss-Prot accession. The leading full-length chloroplast maturase-K sequence has 98.21% global identity, eight substitutions and one gap column. Other hits are much shorter maturase fragments. This supports a qualified sequence-based counterpart while preserving the source sequence and documenting the differences.
MMseqs2 searched 26,379 sequences across UP000836841 at E <= 1e-5 and sensitivity 7.5, returning 6 hits. Every returned sequence was globally aligned using BLOSUM62 with gap-open -10 and extension -0.5. Scores and sequences for all 6 returned candidates are retained, with 6 detailed alignment files. The heuristic search does not establish genomic absence or unique locus identity.
file:THLAR/matK/matK-record-evidence.yaml
target_sequence_count: 26379
file:THLAR/matK/matK-record-evidence.yaml
candidate_count: 6
A0A1U9RZH7: 495 identities across 504 global-alignment columns (98.2143% identity including gaps), 8 substitutions and 1 gap columns. Query coverage is 99.8016%; target coverage is 100.0%. Sequence similarity is interpreted in the manual rationale. Identity over paired residues is 98.4095% (495/503); gap columns are excluded from this denominator.
file:THLAR/matK/matK-record-evidence.yaml
query_length: 504 target_length: 503 alignment_columns: 504 identities: 495 mismatches: 8 gap_columns: 1 identity_percent: 98.2143 query_coverage_percent: 99.8016 target_coverage_percent: 100.0
The primary accession is outside every searched exact-taxon reference proteome. Current UniProt records place A0A1U9RZH7 in UP000836841 and give it the same taxon as the primary.
file:THLAR/matK/matK-record-evidence.yaml
primary_in_any_reference_proteome: false
file:THLAR/matK/matK-record-evidence.yaml
alternative_in_reference_proteome: true
file:THLAR/matK/matK-record-evidence.yaml
same_taxon: true
Sampled UniSave observations: 07-JAN-2015, entry version 46.: no Proteomes cross-reference; 11-DEC-2019, entry version 51.: no Proteomes cross-reference; 22-FEB-2023, entry version 53.: no Proteomes cross-reference. These dated observations do not establish uninterrupted membership/absence, the exact change date, or UniProt's motivation.
file:THLAR/matK/matK-record-evidence.yaml
entry_date: 07-JAN-2015, entry version 46. proteomes: []
file:THLAR/matK/matK-record-evidence.yaml
entry_date: 11-DEC-2019, entry version 51. proteomes: []
file:THLAR/matK/matK-record-evidence.yaml
entry_date: 22-FEB-2023, entry version 53. proteomes: []
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IEA GO_REF:0000117 | MODIFY | Summary: Over-general and redundant. MatK is a plastid genome-encoded protein that localizes to the chloroplast stroma (soluble fraction in transplastomic tobacco); the generic cytoplasm term should be specialized to the chloroplast stroma, consistent with the separate chloroplast annotation. Proposed replacements: chloroplast stroma Supporting Evidence: file:THLAR/matK/matK-deep-research-falcon.md MatK is a chloroplast protein enriched in the soluble fraction (stroma) rather than membranes |
| GO:0006397 mRNA processing | IEA GO_REF:0000002 | ACCEPT | Summary: Acceptable. Several MatK splicing targets are group IIA introns within protein-coding (mRNA) transcripts, including atpF, rpl2 and rps12, so MatK does contribute to mRNA processing. The more precise activity is captured by the group II intron splicing annotation below. Supporting Evidence: file:THLAR/matK/matK-deep-research-falcon.md MatK-dependent group IIA introns include atpF, rpl2 and rps12 intron 2 |
| GO:0008380 RNA splicing | IEA GO_REF:0000104 | MODIFY | Summary: Correct but can be made precise. MatK is specifically a group II intron maturase / splicing factor acting on chloroplast group IIA introns. The dedicated group II intron splicing term is more informative than the generic RNA splicing parent. Proposed replacements: Group II intron splicing Supporting Evidence: file:THLAR/matK/matK-deep-research-falcon.md MatK facilitates splicing (excision) of chloroplast group IIA introns as a trans-acting maturase |
| GO:0009507 chloroplast | IEA GO_REF:0000120 | ACCEPT | Summary: Correct. MatK is plastid genome-encoded and functions in the chloroplast. Consistent with the UniProt subcellular location (Plastid, chloroplast). Supporting Evidence: file:THLAR/matK/matK-deep-research-falcon.md chloroplast-encoded intron maturase localized to the chloroplast stroma |
| GO:0003723 RNA binding | IEA | NEW | Summary: Proposed new molecular-function annotation. GOA currently lists no molecular function for MatK, but the protein is an RNA-binding intron maturase that binds its target group IIA introns to promote splicing; the conserved maturase domain X is an RNA-binding region. This is the core molecular function and should be added. Supporting Evidence: file:THLAR/matK/matK-deep-research-falcon.md Maturases act as cofactors by binding intron RNA to stabilize the correct folded state and promote catalytic steps; MatK associates with multiple intron-containing transcripts in vivo |
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