The first genuine sale of mortgage-backed securities from an Australian issuer this year was launched yesterday when ratings agencies assigned preliminary ratings to a $500 million issue of securities issued by Citigroup through its Securitised Australian Mortgage Trust 2008-1.Standard & Poor's assigned a preliminary rating of AAA to the notes and Moody's gave them a provisional rating of Aaa. The issue is structured as a single tranche. Reflecting current market conditions the issue meets the requirements for Reserve Bank repo eligibility: it is AAA rated, the loans are all prime residential mortgages and the notes are independent of lenders' mortgage insurance.The issue is yet to be priced and Citigroup has not provided any details of investor demand.There are 2622 loans in the pool with an average loan size of $190,787. The maximum loan to valuation ratio is 76.6 per cent and the average is 51.5 per cent. All loans are on variable rates.Citi has provided credit support, through a subordinated tranche, of $25 million - five per cent of the pool. This is twice the level of credit support recommended by S&P.S&P's presale report notes that 90 per cent of Citi's originations come through brokers.Almost three quarters of the loans in the pool are line of credit. Almost 80 per cent of the loans are on interest-only payments. Citigroup services the loans.Citigroup launched its first SAM Trust in 1995 and this is the 10th in the series.UniCredit, a European bank, appeared to undertake a private placement of $750 million of mortgage-backed securities in January, as part of the European bank's role in assisting RHG (formerly Rams) to refinance $6 billion in loans. However, UniCredit is assumed to have been the investor in those securities.