The Office of Financial Research (OFR) (a department of the US Treasury) has published new research "OFR Monitor Shows Accelerating Shift to Government Money Market Funds".
This includes a new US Money Market Fund (MMF) Monitor site which shows the detailed breakdowns of the MMFs by: Region, Country, Sector, Credit and Asset Type.
It shows significant declines this year (approx USD 700 billion) in the size of total Prime MMFs, which can buy non-Government paper including bank paper. The OFR attributes the shift to the Oct. 14, 2016, deadline for implementing Securities and Exchange Commission (SEC) reforms.
This is balanced by a similar growth in Government MMFs. These MMFs can continue to redeem at par but are unable to invest in bank paper.