You cannot transport regulated commodities in interstate commerce (for hire) until you have obtained operating authority (certificate and/or permit) and received your single-state registration. The act of applying for operating authority is not sufficient. You cannot operate until the certificate and/or permit has been issued.
If you are transporting exempt commodities (see below) and have a USDOT number, you may operate as an exempt for-hire interstate motor carrier without an MC number. You are still required to abide by your state regulations.
On our website you will find Administrative Ruling No. 119, which is a guide to what is and is not exempt. The booklet no longer is in print, but the information still is accurate. The list of exempt commodities changes, but this can be used as a general guide. A list of non-exempt commodities can be found in the FMCSR in Section 372.115.