National Center for Biotechnology Information, NIH, DHHS, Bethesda, MD, USA. gertz@ncbi.nlm.nih.gov.|National Center for Biotechnology Information, NIH, DHHS, Bethesda, MD, USA. gertz@ncbi.nlm.nih.gov.|National Center for Biotechnology Information, NIH, DHHS, Bethesda, MD, USA. gertz@ncbi.nlm.nih.gov.|National Center for Biotechnology Information, NIH, DHHS, Bethesda, MD, USA. gertz@ncbi.nlm.nih.gov.|National Center for Biotechnology Information, NIH, DHHS, Bethesda, MD, USA. gertz@ncbi.nlm.nih.gov.|Bioinformatics Research Centre (BIRC), School of Computer Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. zhengjie@ntu.edu.sg.