Table 1.

neXtProt protein existence evidence levels in releases from 2012-02 to 2020-01 showing progress in reducing the PE2,3,4 Missing Proteins, identifying proteins as PE1,^a and approaching a complete protein parts list (adapted from Omenn et al (28), JPR, 2020 and informed by Adhikari et al (12))

Level/date of neXtProt release	2012–02	2013–09	2014–10	2016–01	2017–01	2018–01	2019–01	2020–01
PE1: Evidence at protein level	13,975	15,646	16,491	16,518	17,008	17,470	17,694	17,874
Missing Proteins (MP) = PE2 + PE3 + PE4b	5511	3844	2948	2949	2579	2186	2129	1899
PE2: Evidence at transcript level	5205	3570	2647	2290	1939	1660	1548	1596
PE3: Inferred from homology	218	187	214	565	563	452	510	253
PE4: Predicted	88	87	87	94	77	74	71	50

PE1 = high-quality evidence for expression of the protein in compliance with HPP Guidelines; PE2 = detection of corresponding transcript without sufficient evidence of protein expression; PE3 = evidence of protein in nonhuman species; PE4 = protein predicted from a gene model, all according to neXtProt.

^aPE1/PE1+2 + 3 + 4 = 17,874/19,773 = 90.4%.

^bPE 2 + 3 + 4 = 1899 “missing proteins” as of neXtProt 2020-01 (Jan).