I-485 is still premature at this stage. From
http://www.uscis.gov/files/article/B1eng.pdf :
What if I filed a petition for a relative when I was a permanent resident, but I am now a U.S. citizen?
If you become a U.S. citizen while your relative is waiting for a visa, you can upgrade your relative’s visa classification and advance the processing of that petition by notifying the appropriate agency of your naturalization. When you are a U.S. citizen, your spouse and any unmarried children under age 21 will have visas immediately available to them.
• If you become a U.S. citizen after your Form I-130 petition is already approved and it has been forwarded to the U.S. Department of State’s National Visa Center (NVC), you should notify the NVC that you have become a U.S. citizen. Requests to upgrade petitions due to the naturalization of the petitioner should be sent to:
National Visa Center
32 Rochester Avenue
Portsmouth, NH 03801-2909
Please include a letter with information regarding your relative, a copy of your Naturalization Certificate, and a copy of the petition approval notice. Once the NVC is notified that the petitioner has been naturalized, the NVC will immediately send the visa information on your relative to the designated U.S. Embassy or consulate abroad. To confirm that your approved petition has been forwarded to the NVC, you can contact the NVC’s automated record message system at 1-603-334-0700 and, with a touchtone telephone, enter your USCIS receipt number.
• If you become a U.S. citizen and your relative’s petition has not yet been approved by USCIS, you will need to notify the Service Center where you filed your relative’s visa petition. You should send the notification to the Service Center address located on the receipt notice you received when you filed your Form I-130 petition. Please include a letter with information regarding your relative a copy of your Naturalization Certificate, and a copy of the petition receipt notice. Call Customer Service at 1-800-375-5283 for additional assistance or if you are unsure about the status or location of your petition.
• If your relative is your spouse and he or she has children who are your natural children, stepchildren, or adopted children, and you did not file separate petitions for them, you must file a separate petition for each of them with evidence of your U.S. citizenship. Please include a copy of the receipt notice for the original petition.