hi all. This is the first line from a fasta file.
gi|186681228|ref|YP_001864424.1| phycoerythrobilin:ferredoxin oxidoreductase
What do each word separated by | mean ?
Gene Identifier, RefSeq accession, name of the protein. An in-depth explanation could be found in NCBI's RefSeq handbook.
The first line is a brief description of the sequence. It can contain a number of identifying fields that, as in the example you provide, could be separated by a standard symbol and parsed, or it can contain free text.
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version 2.3.6
gi: gene identifier. ref: refseq accession. Read Chris's answer again, please.
what does gi and ref mean ?
is it compulsory to say gi and ref in the first line ? Cant i just mention the gene identifier and RefSeq without writing gi and ref ?
I'm not sure I understand the motivation of your question. For your internal usage you can put into the fasta header whatever you want; there is no restriction. On the other hand, since RefSeq is a public resource for a broad audience of scientists with different backgrounds, the keywords gi and ref tell the kind of following identifier. Just using a number is ambiguous and it might not be obvious for some people that this references a genbank gene. As for the RefSeq id, the prefix YP_ already implies a RefSeq id. I guess, the 'ref' is there for consistency reasons.