text: Previously, protein markers had been developed using a variety of whole proteins. The development of a kit including a molecular-weight size marker based on protein fragments began in 1993. This protein marker, composed of 49 different amino acid sequences, included multidomain proteins, and allowed for the analysis of proteins cleaved at different sites.
  Current technique improvements in protein markers involve the use of auto-development. The first auto-developed regularly-weight protein marker was invented in 2012.