Comment              mod_base范围限制在修饰碱基缩写词汇表中 

--------------------------------------------------------------------------------

Feature Key           mRNA

Definition           信使RNA；包括5'UTR,CDS,exon,3'UTR区域

Optional qualifiers   /citation=[number]
                      /db_xref="<database>:<identifier>"                     
                      /evidence=<evidence_value>
                      /function="text"
                      /gene="text"
                      /label=feature_label
                      /map="text"
                      /note="text"
                      /partial
                      /product="text"
                      /pseudo
                      /standard_name="text"
                      /usedin=accnum:feature_label

--------------------------------------------------------------------------------

Feature Key           N_region

Definition            在免疫球蛋白片段重排事件中，在其中插入的核苷酸

Optional qualifiers   /citation=[number]
                      /db_xref="<database>:<identifier>"
                      /evidence=<evidence_value>
                      /gene="text"
                      /label=feature_label
                      /map="text"
                      /note="text"
                      /partial
                      /product="text"
                      /pseudo
                      /standard_name="text"
                      /usedin=accnum:feature_label

Parent Key            CDS

Organism scope        Eukaryotes

--------------------------------------------------------------------------------

Feature Key           old_sequence

Definition          现存的序列修正在此位置的以前的版本的序列  

Mandatory qualifiers  /citation=[number]

Optional qualifiers   /db_xref="<database>:<identifier>"
                      /evidence=<evidence_value>
                      /gene="text"
                      /label=feature_label
                      /map="text"
                      /note="text"
                      /partial
                      /replace="text"
                      /usedin=accnum:feature_label

--------------------------------------------------------------------------------

Feature Key           polyA_signal

Definition           RNA转录子的核酸内切酶所必须的识别区域，RNA转录子后带有多聚腺嘌呤，一致序列=AATAA[1]

Optional qualifiers   /citation=[number]
                      /db_xref="<database>:<identifier>"                     
                      /evidence=<evidence_value>
                      /gene="text"
                      /label=feature_label
                      /map="text"
                      /note="text"
                      /partial
                      /usedin=accnum:feature_label

Organism scope        Eukaryotes and eukaryotic viruses

References            [1] Proudfoot, N. and Brownlee, G.G. Nature 263, 211-214 (1976)

--------------------------------------------------------------------------------

Feature Key           polyA_site

Definition            在RNA转录子上通过后转录的多聚腺嘌呤作用加上腺嘌呤的位点

Optional qualifiers   /citation=[number]
                      /db_xref="<database>:<identifier>"                     
                      /evidence=<evidence_value>
                      /gene="text"
                      /label=feature_label
                      /map="text"
                      /note="text"
                      /usedin=accnum:feature_label