On the origin of reverse transcriptase- using CRISPR-Cas systems and their hyperdiverse, enigmatic spacer repertoires

Sukrit Silas, Kira S. Makarova, Sergey Shmakov, David Páez-Espino, Georg Mohr, Yi Liu, Michelle Davison, Simon Roux, Siddharth R. Krishnamurthy, Becky Xu Hua Fu, Loren L. Hansen, David Wang, Matthew B. Sullivan, Andrew Millard, Martha R. Clokie, Devaki Bhaya, Alan M. Lambowitz, Nikos C. Kyrpides, Eugene V. Koonin, Andrew Z. Fire