Sequencing of unknown proteins from a gel can be done by digesting the protein with multiple proteases to obtain overlapping peptides, and using mass spec fragmentation methods to sequence the resulting peptides. It may be difficult to obtain the complete sequence this way, however. Edman degradation can also be used for peptide sequencing instead of mass spec.

It is not necessary to have gene sequence information, but it certainly makes things easier, because the full amino acid sequence can be obtained much more easily from the gene than from peptide sequencing, once the identity of the protein is found from partial peptide sequencing. On the other hand, post-translational modifications will not be observed based only on the gene sequence.

Example:

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