modified. These processes are sufficiently understood to use computer algorithms to automate predictions of protein sequences from DNA sequences, such as from whole-genome DNA-sequencing projects, and have led to the generation of large databases of protein sequences such as UniProt. Predicted protein sequences are an important resource for protein identification by mass spectrometry. Historically, short protein sequences (10 to 15 residues) determined by Edman degradation were back-translated into DNA sequences that could be used as probes or primers to isolate molecular clones of the corresponding gene or complementary DNA. The sequence of the cloned DNA was then determined and used to deduce the full amino-acid sequence of the protein. Bioinformatics tools Bioinformatics tools exist to assist with interpretation of mass spectra (see de novo peptide sequencing), to compare or analyze protein sequences (see sequence analysis), or search databases using peptide or protein sequences (see BLAST). Applications to cryptography The difficulty of protein sequencing was recently proposed as a basis for creating k-time programs, programs that run exactly k times before self-destructing. Such a thing is impossible to build purely in software because all software is inherently clonable an unlimited number of times. See also Proteomics DNA sequencing Klaus Biemann Donald F. Hunt Matthias Mann John R. Yates References Further reading Cell biology Proteomic sequencing