37 CFR §1.414

1. (a)The United States Patent and Trademark Office will act as a Designated Office or Elected Office for international applications in which the United States of America has been designated or elected as a State in which patent protection is desired.
2. (b)The United States Patent and Trademark Office, when acting as a Designated Office or Elected Office during international processing will be identified by the full title “United States Designated Office” or by the abbreviation “DO/US” or by the full title “United States Elected Office” or by the abbreviation “EO/US”.
3. (c)The major functions of the United States Designated Office or Elected Office in respect to international applications in which the United States of America has been designated or elected, include:
   1. (1)Receiving various notifications throughout the international stage and
   2. (2)National stage processing for international applications entering the national stage under 35 U.S.C. 371.